Drug conjugates for delivering compounds to senescent cells

ABSTRACT

Disclosed are agents (e.g., peptides, polypeptides, proteins, small molecules, antibodies, and antibody fragments that target senescent cells) and methods of their use for imaging senescent cells in vivo and for treating or preventing cancer, age-related disease, tobacco-related disease, or other diseases and disorders related to or caused by cellular senescence in a mammal. The methods include administering one or more of the agents of the invention to a mammal, e.g., a human. The agents, which specifically bind to senescent cells, can be labeled with a radioactive label or a therapeutic label, e.g., a cytotoxic agent.

This application is Continuation of U.S. patent application Ser. No. 14/750,941, filed Jun. 25, 2015, which is a Divisional of U.S. application Ser. No. 14/557,316, filed Dec. 1, 2014, which is a Continuation of U.S. application Ser. No. 12/809,952, filed Feb. 21, 2012, which is a U.S. national stage entry under 35 USC 371(c) of PCT/US 2008/13913, filed Dec. 19, 2008, which claims priority to U.S. Provisional Application No.: 61/015,416, filed Dec. 20, 2007, the contents of which are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to compositions and methods for the detection and treatment of cancer, age-related diseases, tobacco-related diseases, and other diseases and disorders related to or caused by cellular senescence.

BACKGROUND OF THE INVENTION

The definition of cellular senescence has undergone some revision since the phenomenon was described by Leonard Hayflick as cessation of replication of cultured human cells after a finite number of population doublings (Hayflick et al., Exp. Cell Res. 37:585-621, 1961). Senescent cells remain metabolically active but do not divide and resist apoptosis for long periods of time (Goldstein, Science 249:1129-1133, 1990). Cellular senescence is characterized by growth cycle arrest in the G1 phase, absence of S phase, and lifespan control by multiple dominant genes (Stanulis-Praeger, Mech. Ageing Dev. 38:1-48, 1987).

Cellular senescence differs from quiescence and terminal differentiation in several important aspects. Senescent cells have characteristic morphological changes such as enlargement, flattening, and increased granularity (Dimri et al., Proc. Nat. Acad. Sci. USA 92:9363-9367, 1995). Senescent cells do not divide even if stimulated by mitogens (Campisi, Trends Cell Biol. 11:S27-S31, 2001). Senescence involves activation of p53 and/or Rb and their regulators such as p16^(INK4a), p21, and ARF. Except when p53 or Rb is inactivated, senescence is irreversible. Senescent cells express increased levels of plasminogen activator inhibitor (PAI) and exhibit staining for β-galactosidase activity at pH 6 (Sharpless et al., J. Clin. Invest. 113:160-168, 2004). Irreversible G1 arrest is mediated by inactivation of cyclin dependent kinase (CdK) complexes which phosphorylate Rb. P21 accumulates in aging cells and inhibits CdK4-CdK6. P16 inhibits CdK4-CdK6 and accumulates proportionally with β-galactosidase activity and cell volume (Stein et al., Mol. Cell. Biol. 19:2109-2117, 1999). P21 is expressed during initiation of senescence but need not persist; p16 expression helps maintain senescence once initiated.

Replicative senescence, the type of senescence originally observed by Hayflick, is related to the progressive shortening of telomeres with each cell division. Senescence is induced when certain chromosomal telomeres reach a critical length (Mathon and Lloyd, Nat. Rev. Cancer 3:203-213, 2001; Martins, U. M. Exp Cell Res. 256:291-299, 2000). Senescence can be abrogated by the expression of telomerase which lengthens telomeres; human fibroblasts undergo replication indefinitely when transfected to express telomerase. Most cancers express telomerase in order to maintain telomere length and replicate indefinitely. The minority of cancers that do not express telomerase have alternative lengthening of telomere (ALT) mechanisms.

Indirect evidence suggests some relationship between replicative senescence and aging. Cultured cells from old donors exhibit senescence after fewer population doublings than cells from young donors (Martin et al., Lab. Invest. 23:86-92, 1970; Schneider et al., Proc. Nat. Acad. Sci. USA 73:3584-3588, 1976). Cells from short-lived species senesce after fewer population doublings than cells from long-lived species (Rohme, D., Proc. Nat. Acad. Sci. USA 78:5009-3320, 1981). Cultured cells from donors with hereditary premature aging syndromes such as Werner's syndrome show senescence after fewer replications than cells from age-matched controls (Goldstein, Genetics of Aging, 171-224, 1978; Martin, Genetic Effects on Aging, 5-39, 1990). Whether replicative senescence actually contributes to aging or age-related symptoms in vivo is questionable on the basis of theoretical estimates of the number of cell divisions that occur in vivo and the absence of strong empirical evidence.

There are, however, other pathways to senescence than replication. Collectively, these are often referred to as stress-induced premature senescence (SIPS). Oxidative stress can shorten telomeres (von Zglinicki, Trends Biochem. Sci. 27:339-344, 2002) and hyperoxia has been shown to induce senescence. Gamma irradiation of human fibroblasts in early to mid G1 phase causes senescence in a p53-dependent manner (Di Leonardo et al., Genes Dev. 8:2540-2551, 1994). Ultraviolet radiation also induces cellular senescence. Other agents that can induce cellular senescence include hydrogen peroxide (Krtolica et al., Proc. Nat. Acad. Sci. USA 98:12072-12077, 2001), sodium butyrate, 5-azacytadine, and transfection with the Ras oncogene (Tominaga, Mech. Ageing Dev. 123(8):927-936, 2002). Chemotherapeutic agents including doxorubicin, cisplatin, and a host of others have been shown to induce senescence in cancer cells (Roninson, Cancer Res. 63:2705-2715, 2003). 5-bromodeoxyuridine treatment results in cellular senescence in both normal and malignant cells (Michishita et al., J. Biochem. 126:1052-1059, 1999). Generally speaking, agents that damage DNA can cause cellular senescence. The existence of cellular senescence in vivo has been demonstrated. In a study by Dimri et al., published in 1995, senescent fibroblasts were shown to exhibit staining for β-galactosidase activity at pH 6. These cells failed to incorporate tritiated thymidine and retained β-galactosidase activity after replating but did not divide. Quiescent fibroblasts did not show staining. Keratinocytes, umbilical vein endothelial cells, and mammary epithelial cells all showed increased staining with increased population doublings. Immortalized cells and terminally differentiated keratinocytes did not show staining. Staining was performed on skin biopsies to test whether senescence is observed in vivo. An age-dependent pattern in which an increased number of cells showed staining with increased donor age was observed in the dermis and epidermis (Dimri et al., Proc. Nat. Acad. Sci. USA 92:9363-9367, 1995). The existence of an increase in the number of senescent fibroblasts has been shown in the lungs of subjects with emphysema relative to subjects without emphysema (Müller et al., Resp. Res. 7:32-41, 2006).

Cellular senescence confers a number of functional changes on the cell that likely have clinical relevance. Senescent endothelial cells secrete elevated levels of plasminogen activator inhibitor 1 (PAI-1; Kletsas et al., Ann. N.Y. Acad. Sci. 908:11-25, 2000). Senescent fibroblasts over express collagenase and under express collagenase inhibitors (West et al., Exp Cell Res 184:138-147, 1989). Serial passages of human fibroblasts from a 25 year old donor showed increased elastase endopeptidase type activity (Homsy et al., Journal of Investigative Dermatology 91:472-477, 1988). Endothelial cells obtained from tissue overlying atherosclerotic plaques were observed to have a senescent morphology and express increased levels of PAI-1 and intracellular adhesion molecule 1 and decreased levels of nitric oxide (Davis et al., British Heart Journal 60:459-464, 1988; Arterioscler. Thromb. 11:1678-1689, 1991; Finn et al., Circulation 105:1541-1544, 1976; Comi et al., Exp. Cell Res. 219:304-308, 1995; Chang et al., Proc. Nat. Acad. Sci. USA 92:11190-11194, 1995). Indirect evidence that cellular senescence may play a role in cardiovascular disease also is provided by the observation that shorter leukocyte telomere length is associated with an increased risk of premature myocardial infarction (Brouilette et al., Arteriosclerosis, Thrombosis, and Vascular Biology 23:842-846, 2003).

Cancer cells are immortal, meaning that they can replicate indefinitely without exhibiting senescence. A preponderance of opinion in the scientific community says that the teleological purpose of senescence is to prevent cancer by limiting the number of cell divisions that can occur. This view is supported by experiments in mice showing that p53 knockout results in increased cancer incidence and severity. Indirect evidence that senescence suppresses cancer occurrence includes the observations that oncogenes immortalize or extend cellular lifespan and tumor suppressors Rb and p53, which are critical for senescence, suffer a loss of function mutation in cancer (Shay et al., Biochem. Biophys. Acta. 1071:1-7, 1991).

Senescent cells can also promote tumorigenesis. Senescent stromal cells express tumor promoting as well as tumor suppressing factors that exert a paracrine effect on neighboring epithelial cells; such effects include mitogenicity and antiapoptosis (Chang et al., Proc. Nat. Acad. Sci. USA 97(8):4291-4296, 2000). Senescent fibroblasts have been shown to stimulate premalignant and malignant epithelial cells but not normal epithelial cells to form tumors in mice; this occurred when as few as 10% of the fibroblasts were senescent (Krtolica et al., Proc. Nat. Acad. Sci. USA 98:12072-12077, 2001). Tumor promoting factors secreted by senescent cells are partly mediated by p21^(waf1/cip1/sdi1) (Roninson, Cancer Res. 63:2705-2715, 2003). A threshold of senescent stromal cells appears to provide a milieu allowing adjacent premalignant epithelial cells to survive, migrate, and divide (Campisi, Nat. Rev. Cancer 3:339-349, 2003).

In summary, cellular senescence does occur in vivo and is a likely sequel to environmental insults. Its prevalence increases with age at least in some tissue compartments. Senescence confers functional changes on the cell which have been associated to some degree with various age-related diseases (Chang et al., Proc. Nat. Acad. Sci. USA 97(8):4291-4296, 2000). Senescent cells also contribute to tumor formation. There exists a need for agents that are capable of detecting senescent cells in vivo and for treating or preventing diseases and disorders related to or caused by cellular senescence.

SUMMARY OF THE INVENTION

This invention features compositions and methods for the detection and imaging of senescent cells in vitro or in vivo in order to predict the risk of diseases or disorders related to or caused by cellular senescence (e.g., cancer occurrence, cancer metastasis, cardiovascular disease, cerebrovascular disease, Alzheimer's disease, and emphysema). The invention also features compositions and methods for treating, preventing, or inhibiting the development or progression of diseases or disorders related to or caused by cellular senescence (e.g., by administering an agent that results in the death and removal of one or more, all, or substantially all senescent cells or cells expressing one or more senescence markers from an organism). The compositions and methods can be administered in order to prevent, ameliorate, inhibit the development of, or treat diseases or disorders related to or caused by cellular senescence (e.g., cancer, cardiovascular disease, cerebrovascular disease, Alzheimer's disease, emphysema, osteoarthritis, and other age-related diseases). The invention features peptides which bind with higher affinity to senescent cells than non-senescent cells.

In a first aspect, the invention features a peptide, polypeptide, antibody, or antibody fragment agent having an amino acid sequence set forth in any one of SEQ ID NOS:1-3 and 5-8 or a peptide, polypeptide, antibody, antibody fragment, or small molecule agent that is capable of specifically binding to an antigen having an amino acid sequence having at least 20 amino acids with at least 80% sequence identity to any one of the amino acid sequences set forth in SEQ ID NOS:11-23. In one embodiment, the antigen has an amino acid sequence having at least 20 amino acids of any one of the amino acid sequences set forth in SEQ ID NOS:11-23. In another embodiment, the antigen has any one of the amino acid sequences set forth in SEQ ID NOS:11-23.

In embodiments of the first aspect of the invention, the agent includes a detectable label, a therapeutic agent, a chelating agent, or a linker moiety. An agent of the first aspect of the invention can be indirectly or directly attached to the detectable label. The linker moiety can have the amino acid sequence GGGC, GGGS, or GG. A detectable label can be a radioactive agent, fluorescent agent, bioluminescent molecule, epitope tag, or heavy metal. Radioactive agents include iodine, astatine, and bromine labels that are attached to an amino acid of an agent of the first aspect of the invention. A radioactive agent can also be technetium-99m. Fluorescent agents include fluorescein isothiocyanate (FITC), allophycocyanin (APC), phycoerythrin (PE), rhodamine, tetramethyl rhodamine isothiocyanate (TRITC), fluorescent protein (GFP), enhanced GFP (eGFP), yellow fluorescent protein (YFP), cyan fluorescent protein (CFP), red fluorescent protein (RFP), and dsRed. A bioluminescent molecule can be luciferase. Epitope tags include c-myc, hemagglutinin, and histidine tags. A therapeutic agent can be a cytotoxic agent, such as an alkylating agent, an antibiotic, an antineoplastic agent, an antimetabolic agent, a ribosomal activity inhibitor, an antiproliferative agent, a tubulin inhibitor, a topoisomerase I or II inhibitor, a growth factor, an hormonal agonist or antagonists, an apoptotic agent, an immunomodulator, a radioactive agent, a phospholipase, or a cytotoxic peptide or lysin. A cytotoxic agent can also be ricin, doxorubicin, methotrexate, camptothecin, homocamptothecin, thiocolchicine, colchicine, combretastatin, combretastin A-4, podophyllotoxin, rhizoxin, rhizoxin-d, dolistatin, paclitaxel, CC1065, ansamitocin p3, maytansinoid, streptolysin O, stoichactis toxin, phallolysin, staphylococcus alpha toxin, holothurin A, digitonin, melittin, lysolecithin, cardiotoxin, cerebratulus A toxin, or any derivative thereof. A chelating agent joined to an agent of the first aspect of the invention can be an ininocarboxylic reactive group, a polyaminopolycarboxylic reactive group, diethylenetriaminepentaacetic acid (DTPA), or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). In any embodiment, the agent of the first aspect of the invention can further include a pharmaceutically acceptable carrier. An agent of the first aspect of the invention can specifically bind to a senescent cell, such as a senescent lung, breast, colon, prostate, gastric, hepatic, ovarian, esophageal, or bronchial epithelial or stromal cell, a senescent skin epithelial or stromal cell; a senescent glial cell; or a senescent vascular endothelial or stromal cell.

In a second aspect, the invention features a method of imaging a senescent cell-containing region in a mammal, such as a human, in vivo, by administering to the mammal an agent of the first aspect of the invention that is joined to a detectable label, allowing the agent to bind senescent cells and allowing unbound agent to be cleared from the body of said mammal, and obtaining an image of the senescent cell-containing region. Senescent cell-containing regions include the breast, prostate, gastrointestinal tract, liver, lungs, intracranial space, nasopharynx, oropharynx, larynx, esophagus, mediastinum, abdomen and pelvis, any region of the body containing peripheral vasculature, and the entire body. An image of the senescent cell-containing region can be obtained by scintigraphy.

In a third aspect, the invention features a method of predicting cancer risk in a mammal, such as a human, by administering to the mammal an agent of the first aspect of the invention that is joined to a detectable label and predicting an elevated cancer risk in the mammal by detecting binding of the agent to a senescent cell of the mammal. The method can be used to predict the risk of prostate cancer, colon cancer, lung cancer, squamous cell cancer of the head and neck, esophageal cancer, hepatocellular carcinoma, gastric cancer, pancreatic cancer, ovarian cancer, and breast cancer.

In a fourth aspect, the invention features a method of treating or preventing disease in a mammal, such as a human, by administering to the mammal an agent of the first aspect of the invention joined to a cytotoxic agent.

In a fifth aspect, the invention features a method of treating or preventing disease in a mammal, such as a human, by administering to the mammal a nucleic acid molecule encoding a cytotoxic agent and an agent of the first aspect of the invention. The nucleic acid molecule can be administered in a vector, such as an adenoviral vector. In one embodiment, the cytotoxic agent and agent of the first aspect of the invention are expressed as a single polypeptide chain.

In either the fourth or fifth aspects of the invention, diseases that can be treated or prevented include cancer, age-related diseases, tobacco-related diseases, and skin wrinkles. Cancers that can be treated or prevented include prostate cancer, colon cancer, lung cancer, squamous cell cancer of the head and neck, esophageal cancer, hepatocellular carcinoma, gastric cancer, pancreatic cancer, ovarian cancer, and breast cancer. Age-related or tobacco-related diseases include cardiovascular disease, cerebrovascular disease, peripheral vascular disease, Alzheimer's disease, osteoarthritis, cardiac diastolic dysfunction, benign prostatic hypertrophy, aortic aneurysm, and emphysema.

In a sixth aspect, the invention features a method for identifying a peptide or polypeptide capable of detecting senescent cells by (a) culturing cells to produce senescent cells, (b) exposing the senescent cells to a phage peptide library, (c) recovering the senescent cells and phage from said phage peptide library bound to said senescent cells, (d) eluting and amplifying bound phage to produce amplified phage, (e) repeating steps (a)-(d) one or more times, and (f) recovering a peptide or polypeptide expressed by the amplified phage that is capable of detecting senescent cells.

In a seventh aspect, the invention features a method for identifying an antibody or antibody fragment capable of specifically binding to a senescent cell-specific antigen by contacting an antibody or antibody fragment with a polypeptide having at least 20 amino acids having at least 80% amino acid sequence identity to any one of the amino acid sequences set forth in SEQ ID NOS:11-23, and identifying an antibody or antibody fragment that binds the polypeptide with a dissociation constant of less than 10⁻⁷ M.

In an eighth aspect, the invention features a method for identifying an antibody or antibody fragment capable of specifically binding to a senescent cell-specific antigen by administering a polypeptide having at least 20 amino acids having at least 80% amino acid sequence identity to any one of the amino acid sequences set forth in SEQ ID NOS:11-23 to a mammal, allowing the mammal to generate a humoral immune response to the polypeptide, and identifying an antibody or antibody fragment that binds the polypeptide with a dissociation constant of less than 10⁻⁷ M. Mammals suitable for the identification of antibodies that specifically bind senescent cell-specific antigens include mice, hamsters, rats, guinea pigs, chickens, goats, sheep, cows, horses, non-human primates, and humans.

In an ninth aspect, the invention features a method for identifying a small molecule capable of specifically binding to a senescent cell-specific antigen by contacting a small molecule with a polypeptide having at least 20 amino acids having at least 80% amino acid sequence identity to any one of the amino acid sequences set forth in SEQ ID NOS:11-23 and identifying a small molecule that binds the polypeptide with a dissociation constant of less than 10⁻⁷M.

In an tenth aspect, the invention features a method of making an antibody or antibody fragment by recombinantly expressing a nucleic acid sequence that encodes an amino acid sequence having one or more of SEQ ID NOs:1-3 and 5-8, wherein the antibody or antibody fragment specifically binds a senescent cell.

In an eleventh aspect, the invention features a method of cellular therapy performed by administering to a mammal, such as a human, in need thereof an agent of the invention prior to, concurrent with, or following administration of a cellular therapeutic.

In an twelfth aspect, the invention features a method of cellular therapy performed by contacting an agent of the invention to a donor cell, tissue, or organ prior to, concurrent with, or following administration of the cell, tissue, or organ to a mammal, such as a human. A donor cell, tissue, or organ can be an autologous, allogeneic, syngeneic, or xenogeneic cell, tissue, or organ. A donor cell can be a stem cell, such as a hematopoietic, umbilical cord blood, totipotent, multipotent, or pluripotent stem cell.

In a thirteenth aspect, the invention features a kit containing an agent of the invention and one or more of a detectable label, a therapeutic agent, a chelating agent, or a linker moiety.

The term “about” is used herein to mean a value that is ±10% of the recited value.

By “administration” or “administering” is meant a method of providing a dosage of an agent of the invention to a mammal (e.g., a human), where the route is, e.g., topical, oral, parenteral (e.g., intravenous, intraperitoneal, intrarterial, intradermal, intramuscular, or subcutaneous injection, inhalation, optical drops, or implant), nasal, vaginal, rectal, or sublingual application in admixture with a pharmaceutically acceptable carrier adapted for such use. The preferred method of administration can vary depending on various factors, e.g., the components of the pharmaceutical composition, site of the potential or actual disease (e.g., the location of lung, breast, colon, prostate, liver, brain, heart, etc.), and the severity of disease.

By “analog” is meant an agent that differs from, but is structurally, functionally, and/or chemically related to the reference agent. The analog may retain the essential properties, functions, or structures of the reference agent. Most preferably, the analog retains at least one biological function of the reference agent. Generally, differences are limited so that the structure or sequence of the reference agent and the analog are similar overall. For example, a peptide analog and its reference peptide may differ in amino acid sequence by one or more amino acid substitutions, additions, and/or deletions, or the presence of one or more non-naturally occurring amino acid residues, in any combination. An analog of a peptide or polypeptide of the invention may be naturally occurring, such as an allelic variant, or it may be a variant that is not known to occur naturally. Non-naturally occurring analogs of peptides may be made by direct synthesis, by modification, or by mutagenesis techniques.

By “chelating agent” is meant a molecule that forms multiple chemical bonds with a single metal atom. Prior to forming the bonds, the chelating agent has more than one pair of unshared electrons. The bonds are formed by sharing pairs of electrons with the metal atom. Chelating agents include, for example, an iminodicarboxylic group or a polyaminopolycarboxylic group. Chelating agents may be attached to an agent of the invention using the methods generally described in Liu et al., Bioconjugate Chem. 12(4):653, 2001; Alter et al., U.S. Pat. No. 5,753,627; and PCT Publication No. WO 91/01144; each of which is hereby incorporated by reference). An agent of the invention may be complexed, through its attached chelating agent, to a detectable label, thereby resulting in an agent that is indirectly labeled. Similarly, cytotoxic or therapeutic agents, may also be attached via a chelating group to an agent of the invention.

By “coupled” is meant the characteristic of a first molecule being joined to a second molecule by a covalent bond or through noncovalent intermolecular attraction.

By “cytotoxic agent” is meant any naturally occurring, modified, or synthetic compound that is toxic to cells. Such agents are useful in the treatment of neoplasms, and in the treatment of other symptoms or diseases characterized by cell proliferation or a hyperactive cell population. Cytotoxic agents can also be used to target undesirable cells or tissues other than neoplastic cells or tissues, e.g., senescent cells. Cytotoxic agents include, but are not limited to, alkylating agents, antibiotics, antimetabolites, tubulin inhibitors, topoisomerase I and II inhibitors, hormonal agonists or antagonists, immunomodulators, or agents that cause cell lysis including naturally occurring or synthetic peptides. Cytotoxic agents may be cytotoxic when activated by light or infrared (Photofrin, IR dyes; Nat. Biotechnol. 19(4):327-331, 2001), may operate through other mechanistic pathways, or be supplementary potentiating agents.

By “detectable label” is meant any type of label which, when attached to an agent of the invention, renders the agent detectable. A detectable label may be toxic or non-toxic, and may have one or more of the following attributes, without restriction: fluorescence (Kiefer et al., WO 9740055), color, toxicity (e.g., radioactivity, e.g., a γ-emitting radionuclide, Auger-emitting radionuclide, β-emitting radionuclide, an α-emitting radionuclide, or a positron-emitting radionuclide), radiosensitivity, or photosensitivity. Although a detectable label may be directly attached, for example, to an amino acid residue of an agent of the invention, or indirectly attached, for example, by being complexed with a chelating group that is attached (e.g., linked via a covalent bond or indirectly linked) to an amino acid residue of an agent of the invention. A detectable label may also be indirectly attached to an agent of the invention by the ability of the label to be specifically bound by a second molecule. One example of this type of an indirectly attached label is a biotin label that can be specifically bound by a second molecule, streptavidin. The second molecule may also be linked to a moiety that allows neutron capture (e.g., a boron cage as described in, for example, Kahl et al., Proc. Natl. Acad. Sci. USA 87:7265-7269, 1990).

A detectable label may also be a metal ion from heavy elements or rare earth ions, such as Gd³⁺, Fe³⁺, Mn³⁺, or Cr²⁺ (see, e.g., Curter, Invest. Radiol. 33(10):752-761, 1998). Preferred radioactive detectable labels are radioactive iodine labels (e.g., ¹²²I, ¹²³I, ¹²⁴I, ¹²⁵I, or ¹³¹I) that are capable of being coupled to each D- or L-Tyr or D- or L-4-amino-Phe residues present in the agents of the invention. Preferred non-radioactive detectable labels are the many known dyes that are capable of being coupled to NH₂-terminal amino acid residues.

Preferred examples of detectable labels that may be toxic to cells include ricin, diphtheria toxin, and radioactive detectable labels (e.g., ¹²²I, ¹²³I, ¹²⁴I, ¹²⁵I, ¹³¹I, ¹⁷⁷Lu, ⁶⁴Cu, ⁶⁷Cu, ¹⁵³Sm, ¹⁶⁶Ho, ¹⁸⁶Re, ¹⁸⁸Re, ²¹¹At, ²¹²Bi, ²²⁵Ac, ⁶⁷Ga, ⁶⁸Ga, ⁷⁵Br, ⁷⁶Br, ⁷⁷Br, ^(117m)Sn, ⁴⁷Sc, ¹⁰⁹Pd, ⁸⁹Sr, ¹⁵⁹Gd, ¹⁴⁹Pm, ¹⁴²Pr, ¹¹¹Ag, ¹⁶⁵Dy, ²¹³Bi, ¹¹¹In, ^(114m)In, ²⁰¹Ti, ^(195m)Pt, ¹⁹³Pt, ⁸⁶Y and ⁹⁰Y). These compounds, and others described herein may be directly or indirectly attached to an agent of the invention or its analogs. A toxic detectable label may also be a chemotherapeutic agent (e.g., camptothecins, homocamptothecins, 5-fluorouracil or adriamycin), or may be a radiosensitizing agent (e.g., paclitaxel, gemcitabine, fluoropyrimidine, metronitozil, or the deoxycytidine analog 2′,2′ difluoro-2′-deoxycytidine (dFdCyd) to which is directly or indirectly attached an agent or analog thereof of the present invention.

A detectable label, when coupled to an agent of the invention emits a signal that can be detected by a signal transducing machine. In some cases, the detectable label can emit a signal spontaneously, such as when the detectable label is a radionuclide. In other cases the detectable label emits a signal as a result of being stimulated by an external field such as when the detectable label is a relaxivity metal. Examples of signals include, without limitation, gamma rays, X-rays, visible light, infrared energy, and radio waves. Examples of signal transducing machines include, without limitation, gamma cameras including SPECT/CT devices, PET scanners, fluorimeters, and Magnetic Resonance Imaging (MRI) machines.

By “diagnostically effective amount” is meant a dose of detectably-labeled agent that, when administered internally to a mammal, is quantitatively sufficient to be detected by a signal transducing machine external to the mammal (e.g., a gamma camera used in gamma scintigraphy) but typically is quantitatively insufficient to produce a pharmacological effect.

By “imaging agent” is meant a compound that, when administered to a living subject, such as a mammal (e.g., a human), allows the visualization of internal structures (e.g., cells, tissues, and organs) and, in some cases can provide information as to the function of a cell, tissue, or organ in the subject.

By “linker moiety” is meant a sequence of amino acid residues, e.g., at least one, two, three, four, five, six, seven, eight, nine, ten, fifteen, twenty, thirty, forty, fifty, or more residues, that couples an agent of the invention (e.g., a peptide, polypeptide, protein, small molecule, antibody, or antibody fragment that target senescent cells) to, e.g., one or more of a detectable label, a therapeutic agent, and a chelating agent.

By “senescent cell” is meant a cell that is metabolically active but is permanently withdrawn from the cell cycle (see, e.g., Campisi, Cell 120:513-522, 2005). Senescent cells do not replicate and possess one or more of the following additional characteristics attributed to senescent cells: cell cycle arrest in the G1 phase; an enlarged, flattened morphology; increased granularity; staining for β-galactosidase activity at pH 6; senescence associated heterochromatic foci; and characteristic gene expression that is in part regulated by p16 and p21. Alternatively, a senescent cell is a cell that can be induced to become senescent (e.g., by stress) or that expresses cell-surface markers characteristic of senescent cells; these markers include senescent cell-specific antigens having the polypeptide sequences set forth in SEQ ID NOS:11-23. Senesecent cell-specific antigens are those peptides, polypeptides, or glycoproteins that are expressed on the cell surface of senescent cells, but are absent or only weakly expressed on the cell surface of non-senescent cells.

By “peptide” is meant a polymer that includes two or more amino acids joined to each other by a peptide bond or a modified peptide bond. “Peptide” refers to both short chain polymers, commonly referred to as peptides, oligopeptides, or oligomers, having, e.g., about 10-50 linked amino acid residues, and to longer polymers having up to about 100 amino acid residues in length. Peptides may contain amino acids other than the 20 gene-encoded amino acids, and linkages other than peptide bonds and may include cyclic or branched peptides. “Peptides” include amino acid sequences modified either by natural processes, or by chemical modification techniques that are well known in the art. Modifications may occur anywhere in a polypeptide, including the peptide backbone, the amino acid side-chains, and the amino or carboxyl termini.

The notations used herein for the peptide amino acid residues are those abbreviations commonly used in the art. The less common abbreviations Abu, Ava, β-Ala, hSer, Nle, Nva, Pal, Dab, and Dap stand for 2-amino-butyric acid, amino valeric acid, beta-aminopropionic acid, homoserine, norleucine, norvaline, (2,3, or 4) 3-pyridyl-Ala, 1,4-diaminobutyric acid, and 1,3-diaminopropionic acid, respectively. In all aspects of the invention, it is noted that when amino acids are not designated as either D- or L-amino acids, the amino acid is either an L-amino acid or could be either a D- or L-amino acid. Examples of peptides of the invention include those peptides having the sequence of, or a sequence substantially identical to, the sequences set forth in SEQ ID NOs:1-3 and 5-8 and related sequences. These peptide sequences can also be incorporated into a polypeptide, protein, antibody, or antibody fragment.

By “reducing agent” is meant a chemical compound used to reduce another chemical compound by donating electrons, thereby becoming oxidized.

By “specifically binds” is meant that an agent of the invention recognizes and binds to a target (e.g., a senescent cell), but does not substantially recognize and bind to a non-target (e.g., non-senescent cells), both in vivo and in a sample, e.g., an in vitro biological sample, that includes, e.g., senescent cells. A desirable agent of the invention specifically binds to senescent cells. Preferably, the agents of the invention bind senescent cells with at least 2, 5, 10, 20, 100, or 1000 fold greater affinity than they bind to non-senescent cells. Alternatively, agents of the invention specifically bind to senescent cells with a dissociation constant less than 10⁻⁶M, more preferably less than 10⁻⁷M, 10⁻⁸M, 10⁻⁹M, 10⁻¹⁰M, 10⁻¹¹M, or 10⁻¹²M, and most preferably less than 10⁻¹³M, 10⁻¹⁴M, M or 10⁻¹⁵M.

By “substantial sequence identity” or “substantially identical” is meant that a nucleic acid or amino acid sequence exhibits at least 50%, preferably 60%, 70%, 75%, or 80%, more preferably 85%, 90% or 95%, and most preferably 99% identity to a reference amino acid sequence (e.g., one or more of the sequences set forth in SEQ ID NOs:1-3 and 5-8). For amino acid sequences, the length of comparison sequences will generally be at least 5 amino acids, preferably at least 10 contiguous amino acids, more preferably at least 15, 20, 25, 30, 40, 50, 60, 80, 90, 100, 150, 200, 250, 300, or 350 contiguous amino acids, and most preferably the full-length amino acid sequence. Sequence identity is typically measured using BLAST® (Basic Local Alignment Search Tool) or BLAST® 2 with the default parameters specified therein (see, Altschul et al., J. Mol. Biol. 215:403-410, 1990); and Tatiana et al., FEMS Microbiol. Lett. 174:247-250, 1999). This software program matches similar sequences by assigning degrees of homology to various substitutions, deletions, and other modifications. Conservative substitutions typically include substitutions within the following groups: glycine, alanine, valine, isoleucine, leucine; aspartic acid, glutamic acid, asparagine, glutamine; serine, threonine; lysine, arginine; and phenylalanine, tyrosine.

By “therapeutic agent” is meant any compound that is used in the detection, diagnosis or treatment of disease. Such compounds may be naturally-occurring, modified, or synthetic. A therapeutic agent may be, for example, an agent that causes apoptosis or necrosis of a cell (e.g., a senescent cell) in an organism (e.g., a mammal, such as a human), thereby reducing the number of such cells in the organism. Therapeutic agents that reduce the number of senescent cells in an organism may be, e.g., alkylating agents, antibiotics, antimetabolites, hormonal agonists or antagonists, anti- or pro-apoptotic agents, immunomodulators, or supplementary potentiating agents.

By “treating, stabilizing, or preventing cancer” is meant causing a reduction in the size of a tumor or in the number of cancer cells, slowing or preventing an increase in the size of a tumor or in cancer cell proliferation, increasing the disease-free survival time between the disappearance of a tumor or other cancer and its reappearance, preventing an initial or subsequent occurrence of a tumor or other cancer, or reducing an adverse symptom associated with a tumor or other cancer. In a desired embodiment, the percent of tumor or cancerous cells surviving the treatment is at least 20, 40, 60, 80, or 100% lower than the initial number of tumor or cancerous cells, as measured using any standard assay, such as those described herein. Desirably, the decrease in the number of tumor or cancerous cells induced by administration of a compound of the invention is at least 2, 5, 10, 20, or 50-fold greater than the decrease in the number of non-tumor or non-cancerous cells. Desirably, the methods of the present invention result in a decrease of 20, 40, 60, 80, or 100% in the size of a tumor or number of cancerous cells as determined using standard methods. Desirably, at least 20, 40, 60, 80, 90, or 95% of the treated subjects have a complete remission in which all evidence of the tumor or cancer disappears. Desirably, the tumor or cancer does not reappear after more than 5, 10, 15, or 20 years.

By “treating, stabilizing, or preventing age-related diseases” is meant causing a reduction in the number of symptoms, a decrease in severity of any, all, or substantially all of the symptoms, a complete resolution of any, all, or substantially all symptoms, or preventing the occurrence of any, all, or substantially all symptoms associated with one or more of the age-related diseases including, but not limited to, cardiovascular disease, cerebrovascular disease, peripheral vascular disease, Alzheimer's disease, osteoarthritis, cardiac diastolic dysfunction, benign prostatic hypertrophy, and cancers that increase in incidence and prevalence with increasing patient age such as cancer, e.g., breast cancer, prostate cancer, and colon cancer.

By “treating, stabilizing, or preventing tobacco-related diseases” is meant causing a reduction in the number of symptoms, a decrease in severity of any, all, or substantially all of the symptoms, a complete resolution of any, all, or substantially all symptoms, or preventing the occurrence of any, all, or substantially all symptoms associated with one or more of the diseases associated with the use of smoking tobacco as a risk factor, including, but are not limited to, cardiovascular disease, cerebrovascular disease, peripheral vascular disease, aortic aneurysms, emphysema, esophageal cancer, lung cancer, and squamous cell cancers of the head and neck. Tobacco-related diseases also include diseases that are associated with the use of chewing tobacco, such as squamous cell cancers of the mouth.

Other features and advantages of the invention will be apparent from the following description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the cytotoxicity of SenL (SEQ ID NO:4) when tested on senescent fibroblasts, non-senescent fibroblasts, and immortalized prostate epithelial cells. No cell death was observed in immortalized epithelium.

FIG. 2 is a graph showing the results of a WST assay used to measure cell proliferation following treatment with SenL on senescent fibroblasts, non-senescent fibroblasts, and immortalized prostate epithelial cells. The WST-1 assay depends on mitochondrial dehydrogenase levels, and senescent cells have higher mitochondrial mass than their non-senescent counterparts (Martin-Ruiz et al., J. Biol. Chem. 279(17):17826-33, 2004). Consequently, baseline values for senescent cells are higher than for the other cell types. Treatment with SenL showed no significant effect on metabolic activity for any of the three cell types and therefore did not affect cell proliferation rates.

FIG. 3 is a graph showing the cytotoxicity of SenC (SEQ ID NO:5) conjugated to ricin A subunit as tested in senescent fibroblasts, non-senescent fibroblasts, and immortalized prostate epithelial cells. Significantly more senescent cells were killed than non-senescent cells, and no effect was observed on immortalized epithelium.

FIGS. 4A and 4B are fluorescent micrographs showing the specific binding of a peptide agent of the invention. Senescent cell binding peptide SenC (SEQ ID NO:5) was conjugated to fluorescein and contacted with senescent fibroblasts (FIG. 4A) and non-senescent fibroblasts (FIG. 4B). Both images were acquired using 1/60 second exposure time. Senescent cells show perinuclear and cytoplasmic staining, indicating significant internalization. Only faint surface staining is visible on the non-senescent cells.

FIGS. 5A and 5B are immunofluorescent micrographs showing the cell surface expression of cathepsin B on senescent cells (FIG. 5A) and lack of expression on non-senescent cells (FIG. 5B).

DETAILED DESCRIPTION OF THE INVENTION

The invention features agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) capable of specifically binding to senescent cells. Thus, agents of the invention can include, e.g., detectable labels, therapeutic agents, chelating agents, and cytotoxic agents, and can be used in the detection and treatment of diseases and conditions associated with cellular senescence.

In an embodiment, agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be used to produce imaging agents by conjugation to a detectable label and used for medical imaging. Images obtained using an imaging agent of the invention specifically show tissues, organs, and structures in the body (e.g., a human body) that contain senescent cells by means of, e.g., a signal emitted from the location of the cells, tissues, organs, and structures upon specific binding of the imaging agent to the senescent cells. The signal so obtained indicates the presence of senescent cells and allows semi-quantitative estimation of the relative senescent cell content of tissues, organs, or structures. Structures, tissues, or organs that contain a threshold content of senescent cells are at an elevated risk for the subsequent development of diseases or disorders (e.g., cancer). Typically, a subject deemed at risk for the subsequent development of diseases or disorders (e.g., cancer) exhibit an increase of at least 0.5%, more preferably 1, 1.5, 2, 2.5, 5, or 10%, and more preferably at least 15% or more in the level of senescent cells relative to a patient that does not have the disease or disorder. Use of one or more of the imaging agents of the invention allows for the determination of a patient's risk for developing a disease or disorder, such as cancer or a neurodegenerative disease. Patients determined to have an elevated risk of developing cancer or other diseases and disorders related to or caused by cellular senescence by the use of the imaging agents of the invention can be aggressively monitored, and their cellular senescence related disease or disorder (e.g., a cancer) can thereby be detected earlier, facilitating early treatment. Surgical prophylactic treatment can also be administered if necessary.

One or more of the imaging agents of the invention can also be used to determine the senescent cell content in the brain, which may include, e.g., senescent glial cells and senescent cerebrovascular cells, in order to predict the patient's risk of developing, e.g., Alzheimer's disease or cerebrovascular disease. One or more of the imaging agents of the invention can also be used to predict the onset of vascular disease, including cardiovascular disease, by detecting the senescent cell content in one or more vascular structures in a patient. One or more of the imaging agents of the invention can also be used to predict the risk of developing emphysema by determining the senescent cell content in the lungs of a smoker.

One or more of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can also be used to prepare compositions for therapeutic administration (e.g., to treat, stabilize, inhibit the development or progression of, or prevent age-related diseases, tobacco-related diseases, cancer, neurodegenerative diseases, and other diseases and disorders related to or caused by cellular senescence) by coupling of the agents of the invention to, e.g., therapeutic and/or cytotoxic agents. Senescent cells have been observed in skin to make up only a fraction of the stromal cell compartment even in old donors (Dimri et al., Proc. Nat. Acad. Sci. USA 92:9363-9367, 1995) and up to 16% of stromal fibroblasts in patients with emphysema (Bergner, Respiratory Res. 7:32, 2006), but senescent cells can exert clinically significant paracrine effects even when they compose only 10% of the content of stromal cells (Krtolica et al., Proc. Nat. Acad. Sci. USA 98:12072-12077, 2001). Thus, eliminating senescent cells while leaving intact the majority of the cellular compartment from which the senescent cells originate can ablate the harmful paracrine effects of senescent cells. The secretion of elevated levels of collagenase and elastase and depressed levels of collagenase inhibitors by senescent stromal cells implicates them in diseases or conditions that feature breakdown or decrease in structural integrity of the extra cellular matrix, including emphysema, aortic aneurysms, vascular disease, osteoarthritis, and skin wrinkling. Elimination of some, all, or substantially all senescent stromal cells in a patient (e.g., in a tissue or organ of a patient) can attenuate the progression, decrease the symptoms, or prevent the occurrence of these diseases and conditions. Senescent stromal cells have the ability to stimulate tumorigenesis and, by weakening the extracellular matrix, facilitate metastasis. Thus, the elimination of some, all, or substantially all of the senescent stromal cells in a patient (e.g., in a tissue or organ of a patient) can decrease the risk of tumorigenesis and metastasis (e.g., by 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99% or more).

The senescent cell targeting agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be prepared by amino acid coupling using solid phase peptide synthesis (SPPS). As is known in the art, the amino acids to be used as substrates to form the agents of the invention are Fmoc-protected prior to incorporation into a peptide chain (see, e.g., Chanand White, FMOC Solid Phase Peptide Synthesis, A Practical Approach, Oxford University Press, New York, 2003); incorporated herein by reference in its entirety). The standard coupling techniques used to couple the amino acids in order to form the agents of the invention are known in the art (see, e.g., Chan and White, supra). For example, a polyamide-Rink resin can be prepared by loading a polyamide resin with Fmoc-Rink using chemical protocols well known in the art (see, e.g., Chan and White, supra). The first amino acid in the peptide sequence is coupled to the resin after removing Fmoc from the N-terminal amine of the resin using piperidine. Once the coupling is complete, the resin is washed and Fmoc is removed from the coupled amino acid using piperidine. The resin is washed again, and the next amino acid in the sequence is coupled to the previously coupled amino acid. This process is repeated using the necessary amino acids until the desired peptide is formed. Following the coupling of the final amino acid, the Fmoc group is removed using piperidine. The terminal amine can be left as a free amine, or it can be acetylated. The peptide can be cleaved from the resin using trifluoroacetic acid (TFA), triisopropylsilane, and water according to techniques known in the art (see, e.g., Chan and White, supra). The cleaved peptide is then separated from the residue by filtration. The TFA is typically evaporated to dryness followed by precipitation of the peptide with diethyl ether. Typically, the final peptide product is purified using HPLC. Mass spectrometry is used to verify that the desired peptide is obtained. The agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be readily prepared by automated solid phase peptide synthesis using any one of a number of well-known, commercially available automated synthesizers, such as the Applied Biosystems ABI 433A peptide synthesizer.

The agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be labeled for fluorescence detection by labeling the agent with a fluorophore, such as rhodamine or fluorescein, using techniques well known in the art (see, e.g., Lohse et al., Bioconj. Chem. 8:503-509, 1997). The senescent cell targeting agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can also be labeled with a radioactive metal or a relaxivity metal by coupling the agent to a metal chelating agent that chelates a radioactive metal or relaxivity metal. Examples of chelating agents include, but are not limited to, ininocarboxylic and polyaminopolycarboxylic reactive groups, diethylenetriaminepentaacetic acid (DTPA), and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). The chelating agent can be coupled via its amino acid side chain directly to the agents of the invention. Alternatively, an intervening amino acid sequence can be coupled using SPPS to both the agents of the invention and the chelating agent.

Senescent Cell-Specific Antigens

The inventors have discovered that senescent cells express senescent cell-specific antigens. These antigens can be specifically targeted and bound by the diagnostic or therapeutic (e.g., cytotoxic) agents of the invention, as discussed herein. The specific binding of the diagnostic or therapeutic agents of the invention only to senescent cells and not non-senescent cells reduces the incidence of inaccurate diagnoses (e.g., using diagnostic agents) or bystander cell injury (e.g., resulting from cytotoxic agents).

Senescent cell-specific antigens that can be targeted by agents of the invention include, e.g., mutant beta-actin (SEQ ID NO:11; GI: 28336) and beta-actin (ACTB) protein (SEQ ID NO:12; GI: 15277503), which were identified as cell-surface, senescent-specific antigens occurring in both replicatively senescent and stress-induced prematurely senescent cells, drug resistance-related protein LRP (SEQ ID NO:13; GI: 1097308) and major vault protein (MVP; SEQ ID NO:14; GI: 19913410), which were identified as senescence-specific surface proteins in the replicatively senescent cells only, and thyroid hormone binding protein precursor (SEQ ID NO:15; GI: 339647), unnamed protein product (SEQ ID NO:20; GI: 35655), prolyl 4-hydroxylase, beta subunit precursor (P4HB; SEQ ID NO:16; GI: 20070125), chain A, human protein disulfide isomerase (PDI; SEQ ID NO:17; GI: 159162689), electron-transfer-flavoprotein, beta polypeptide (ETFB; SEQ ID NO:18; GI: 4503609), unnamed protein product (SEQ ID NO:21; GI: 158257194), unnamed protein product (SEQ ID NO:22; GI: 158259937), ATP synthase, H⁺ transporting, mitochondrial F1 complex, alpha subunit precursor (SEQ ID NO:19; GI: 4757810), and cathepsin B (CTSB; SEQ ID NO:23), which were identified on the cell surface of stress induced prematurely senescent cells.

Antibodies that specifically bind to the senescent cell-specific antigens described herein are listed in Table 1. These antibodies, and any other polypeptide, antibody, antibody fragment, or small molecule that specifically binds a senescent cell-specific antigen or fragment thereof, can be incorporated in a diagnostic or therapeutic agent of the invention, as discussed herein. In addition, the antibodies listed in Table 1 can be modified, e.g., by humanization, according to known methods, as is discussed below, for use in the diagnosis and treatment of disease in a mammal, e.g., a human. Alternatively, antibodies against the senescent cell-specific antigens described herein for use in the diagnosis and treatment of disease in a mammal, e.g., a human, can be produced according to methods known in the art, as is discussed below.

TABLE I Senescent Cell-Specific Antigen SEQ ID NO: Anti-Senescent Cell-Specific Antigen Antibodies Mutant beta-actin 11 See, e.g., Leavitt et al., Mol Cell Biol. 7: 2467-2476 (1987); Lin et al., PNAS USA 82: 6995-6999(1985). Beta-actin (ACTB) protein 12 Clone AC-15 (mouse anti-human beta-actin antibody); Clone mAbeam 8226 (mouse anti-human beta-actin antibody). Drug resistance-related 13 Clone 1032 (mouse anti-human LRP antibody); rabbit anti-human protein LRP LRP antibody (see, e.g., Kitazono et al., J. Natl. Cancer Inst. 91: 1647-1653 (1999)). Major vault protein (MVP) 14 Clone 1014 (mouse anti-human major vault protein antibody); clone 2Q431(mouse anti-human major vault protein antibody). Thyroid hormone binding 15 See, e.g., Cheng et al., J. Biol. Chem. 262: 11221-11227 (1987). protein precursor Prolyl 4-hydroxylase, beta 16 Clone P4HB (Abeam Cat. No. ab70415; mouse anti-human prolyl subunit precursor (P4HB) 4-hydroxylase, beta subunit precursor antibody). Chain A, human protein 17 Abeam Cat. No. ab48167 (rabbit anti-human PDI antibody); disulfide isomerase (PDI) clone 1D3 (Santa Cruz Cat. No. sc-59640; mouse anti-human PDI antibody). Electron-transfer- 18 Abeam Cat. No. ab73986 (rabbit anti-human ETFP antibody. flavoprotein, beta polypeptide (ETFP) ATP synthase, H⁺ 19 Clone 15H4 (Abeam Cat. No. ab14748; mouse anti-human transporting, mitochondrial ATP5A); see also, e.g., Vantourout et al., Mol. Immunol. 45: 485-492 F1 complex, alpha subunit (2008). precursor Unnamed protein product 20 See, e.g., Pihlajaniemi et al., EMBO J. 6: 643-649 (1987). (GI: 35655) Unnamed protein product 21 See, e.g., Altsehul et al., Nucleic Acids Res. 25: 3389-3402 (GI: 158257194) (1997) Unnamed protein product 22 See e.g., Heidebrecht et al., Mol Cancer Res. 1: 271-9 (2003) (GI: 158259937) Cathepsin B (CTSB) 23 Clone ZZ12 (mouse anti-human cathepsin B antibody); clone S- 12 (goat anti-human cathepsin B antibody). Small Molecules of the Invention

The invention also features small molecules that can be used diagnostically or therapeutically based on their ability to specifically bind senescent cells. For example, small molecules of the invention include those capable of specifically binding to one or more of the senescent cell-specific antigens described herein and those capable of mimicking the physical, chemical, biological, and/or targeting characteristics of SEQ ID NOs:1-3 and 5-8 and peptides that are substantially identical. Small molecules of the invention can be labeled or fused to diagnostic or therapeutic linkers, markers, cytotoxic agents, or other agents of the invention to aid in the diagnosis or treatment of diseases or disorders related to or caused by cellular senescence. Furthermore, small molecules of the invention can specifically bind a polypeptide that has at least 80% (80%, 90%, 95%, 99%, or 100%) amino acid sequence identity to any one of the amino acid sequences set forth in SEQ ID NOS:11-23, or a fragment thereof.

Methods of screening small molecules for binding to senescent cells

The invention also features methods for the high throughput screening (HTS) of candidate small molecule agents of the invention for their ability to bind senescent cells or senescent cell-specific antigens, including, but not limited to, the polypeptides set forth in SEQ ID NOS:11-23, or fragments thereof. Candidate small molecules will also be screened for their ability to specifically bind senescent cells. In general, candidate small molecules preferably bind target sequences with a dissociation constant less than 10⁻⁶ M for further consideration as an agent of the invention.

Senescent cells of any origin can be used in HTS binding assays and methods. In general, fluorescence and luminescence based assays (e.g., ELISA, colorimetric assays) are used to measure binding affinities of candidate small molecules contacted against single or multiple target senescent cells. Upon the identification of a candidate small molecule from a first screening process, further scrutiny of the binding affinity and ability of the candidate small molecule can be by means of a second, different HTS assay. This could be accomplished, for example, by contacting the candidate small molecule with alternate senescent cell populations to more precisely determine the binding affinity of the molecule. A discussion of HTS methodologies is found in, e.g., Verkman, “Drug discovery in academia,” Am. J. Physiol. Cell Physiol. 286, C465-C474 (2004) and Dove, “Screening for content—the evolution of high throughput,” Nat. Biotechnol. 21:859-864 (2003). Examples of HTS screening methods for the discovery of useful small molecule agents are found in, e.g., U.S. Pat. Nos. 7,279,286 and 7,276,346, which are incorporated by reference herein.

Candidate small molecules that have undergone HTS screening may be further modified to empirically improve senescent cell binding affinities according to the design considerations discussed below.

Small Molecule Design

Small molecules of the invention can also be generated according to the principles of rational design. Computer modeling technology allows visualization of the three-dimensional atomic structure of a selected molecule and the design of new compounds that will interact with senescent cells or senescent cell-specific antigens (e.g., the senescent cell-specific antigens discussed above (set forth in SEQ ID NOS:11-23), or fragments thereof). The three-dimensional construct typically depends on data from x-ray crystallographic analyses or NMR imaging of the selected molecule or epitope. A computer graphics system enables prediction of how a candidate small molecule compound will bind to the target senescent cell and allows experimental manipulation of the structures of the small molecule and target protein to perfect binding specificity. A prediction of what the molecule-protein interaction will be when small changes are made in one or both can be determined by using molecular mechanics software and computationally intensive computers. An example of a molecular modeling system described generally above includes the CHARMm and QUANTA programs (Polygen Corporation, Waltham, Mass.). CHARMm performs the energy minimization and molecular dynamics functions, while QUANTA performs the construction, graphic modeling and analysis of molecular structure. QUANTA allows interactive construction, modification, visualization, and analysis of the behavior of molecules that intact with each other. Another molecular modeling program that can be used to identify small molecules for use in the methods of the invention is DOCK (Kuntz Laboratory, UCSF).

Small Molecule Synthesis

Small molecules of the invention can be organic or inorganic compounds, and even nucleic acids. Specific binding to senescent cells can be achieved by including chemical groups having the correct spatial location and charge in the small molecule. In a preferred embodiment, compounds are designed with hydrogen bond donor and acceptor sites arranged to be complementary to the targeted molecule or epitope. An agent is formed with chemical side groups ordered to yield the correct spatial arrangement of hydrogen bond acceptors and donors when the agent is in a specific conformation induced and stabilized by binding to the target molecule or epitope. Additional binding forces such as ionic bonds and Van der Waals interactions can also be considered when synthesizing a small molecule of the invention. The likelihood of forming the desired conformation can be refined and/or optimized using molecular computational programs.

Organic compounds can be designed to be rigid, or to present hydrogen bonding groups on edge or plane, which can interact with complementary sites. Rebek, Science 235, 1478-1484 (1987) and Rebek et al., J. Am. Chem. Soc. 109, 2426-2431 (1987) have summarized these approaches and the mechanisms involved in binding of compounds to regions of proteins.

Synthetic methods can be used by one skilled in the art to make small molecules that interact with functional groups of proteins, glycoproteins, or epitopes present on the exterior or in the interior of senescent cells.

Preparation of Antibody Compositions of the Invention

The invention also provides antibody compositions that include one or more of the sequences set forth in SEQ ID NOS:1-3 and 5-8, and peptides substantially identical thereto, which can be included in, e.g., one or more of the complementarity determining regions (CDRs) of the antibody compositions. The invention further provides antibody compositions that specifically bind a senescent cell-specific antigen having at least 80% (e.g., 80%, 90%, 95%, 99%, or 100%) amino acid sequence identity to any one of the senescent cell-specific antigens set forth in SEQ ID NOS:11-23, or a fragment thereof.

The antibodies of the invention may be recombinant (e.g., chimeric or humanized), synthetic, or naturally occurring. Antibodies or antibody fragments of the invention can be recombinantly produced, or identified and isolated from a mammal that has been induced to produce or that naturally-produces antibodies that specifically bind to senescent cell-specific antigens. For example, a polypeptide having at least 80% (e.g, 85%, 90%, 95%, 99%, or 100%) amino acid sequence identity to one of the senescent cell-specific antigens set forth in SEQ ID NOS:11-23 can be administered (e.g., by injection) to a mammal (e.g., a mouse, rat, hamster, guinea pig, sheep, goat, cow, horse, non-human primate, or human) to provoke a humoral immune response against the immunizing senescent cell-specific antigen. Blood, plasma, or ascites from the immunized mammal can be screened to identify or harvest antibodies that specifically bind the immunizing senenescent cell-specific antigen. If desired, the amino acid and/or nucleic acid sequences of the antibodies produced can be determined. Furthermore, all or a portion of the nucleic acid sequences of the antibodies can be incorporated into a vector (e.g., an expression vector or a viral vector) for expression of the antibody in a cell of a subject (e.g., a mammal, such as a human) following administration of the vector to the subject, or any other uses consistent with the methods described herein.

The invention features complete antibodies, diabodies, bi-specific antibodies, antibody fragments, Fab fragments, F(ab′)2 molecules, single chain Fv (scFv) molecules, tandem scFv molecules, or antibody fusion proteins. Antibodies of the invention include, e.g., the IgG, IgA, IgM, IgD, and IgE isotypes. Antibodies of the invention contain one or more CDRs or binding peptides that bind to proteins, glycoproteins, or epitopes present on the exterior or in the interior of senescent cells.

Many of the antibodies, or fragments thereof, described herein can undergo non-critical amino-acid substitutions, additions or deletions in both the variable and constant regions without loss of binding specificity or effector functions, or intolerable reduction of binding affinity (i.e., below about 10⁻⁷ M). Usually, an antibody incorporating such alterations exhibits substantial sequence identity to a reference antibody from which it is derived. Occasionally, a mutated antibody can be selected having the same specificity and increased affinity compared with a reference antibody from which it was derived. Phage-display technology offers powerful techniques for selecting such antibodies. See, e.g., Dower et al. (WO 91/17271), McCafferty et al. (WO 92/01047), and Huse (WO 92/06204), each of which is incorporated by reference herein.

Antibody Fragments

In another embodiment of the invention, an agent of the invention is a fragment of an intact antibody described herein. Antibody fragments include separate variable heavy chains, variable light chains, Fab, Fab′, F(ab′)₂, Fabc, and Fv. Fragments can be produced by enzymatic or chemical separation of intact immunoglobulins. For example, a F(ab′)₂ fragment can be obtained from an IgG molecule by proteolytic digestion with pepsin at pH 3.0-3.5 using standard methods such as those described in Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Pubs., N.Y. (1988). Fab fragments may be obtained from F(ab′)₂ fragments by limited reduction, or from whole antibody by digestion with papain in the presence of reducing agents. Fragments can also be produced by recombinant DNA techniques. Segments of nucleic acids encoding selected fragments are produced by digestion of full-length coding sequences with restriction enzymes, or by de novo synthesis. Often fragments are expressed in the form of phage-coat fusion proteins. This manner of expression is advantageous for affinity-sharpening of antibodies.

Humanized Antibodies

The invention also includes humanized antibodies in which one or more of the CDRs are derived from a non-human antibody sequence (e.g., those antibodies described in Table 1), and one or more, but preferably all, of the CDRs bind specifically to a protein, glycoprotein, or epitope present on the exterior or in the interior of a senescent cell (e.g., the senescent cell-specific antigens described above (SEQ ID NOS:11-23), or a fragment thereof).

A humanized antibody contains constant framework regions derived substantially from a human antibody (termed an acceptor antibody), as well as, in some instances, a majority of the variable region derived from a human antibody. One or more of the CDRs (all or a portion thereof, as well as discreet amino acids surrounding one or more of the CDRs) are provided from a non-human antibody, such as a mouse antibody. The constant region(s) of the antibody, may or may not be present. Humanized antibodies provide several advantages over non-humanized antibodies for therapeutic or diagnostic use in humans. These include:

1) The human immune system should not recognize the framework or constant region of the humanized antibody as foreign, and therefore the antibody response against such an injected antibody should be less than against a totally foreign mouse antibody or a partially foreign chimeric antibody;

2) Because the effector portion of the humanized antibody is human, it may interact better with other parts of the human immune system; and

3) Injected mouse antibodies have been reported to have a much shorter half-life in the human circulation than the half-life exhibited by normal human antibodies (see, e.g., Shaw et al., J. Immunol. 138:4534-4538 (1987)). Injected humanized antibodies have a half-life essentially equivalent to naturally occurring human antibodies, allowing smaller and less frequent doses.

The substitution of one or more, e.g., mouse CDRs into a human variable domain framework is most likely to result in retention of their correct spatial orientation if the human variable domain framework adopts the same or similar conformation to the mouse variable framework from which the CDRs originated. This is achieved by obtaining the human variable domains from human antibodies whose framework sequences exhibit a high degree of sequence identity with the murine variable framework domains from which the CDRs were derived. The heavy and light chain variable framework regions can be derived from the same or different human antibody sequences. The human antibody sequences can be the sequences of naturally occurring human antibodies or can be consensus sequences of several human antibodies. See, e.g., Kettleborough et al., Protein Engineering 4:773 (1991); Kolbinger et al., Protein Engineering 6:971 (1993).

Suitable human antibody sequences are identified by computer comparisons of the amino acid sequences of the mouse variable regions with the sequences of known human antibodies. The comparison is performed separately for heavy and light chains but the principles are similar for each.

Methods of preparing chimeric and humanized antibodies and antibody fragments are described in U.S. Pat. Nos. 4,816,567, 5,530,101, 5,622,701, 5,800,815, 5,874,540, 5,914,110, 5,928,904, 6,210,670, 6,677,436, and 7,067,313 and U.S. Patent Application Nos. 2002/0031508, 2004/0265311, and 2005/0226876. Preparation of antibody or fragments thereof is further described in U.S. Pat. Nos. 6,331,415, 6,818,216, and 7,067,313. Each of these patents is incorporated herein by reference.

Diagnostic Agents Coupled to Agents of the Invention

Agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be joined or coupled to any molecule that can be used to label, detect, identify, screen, or diagnose senescent cells in a mammal (e.g., a human). Diagnostic and therapeutic (e.g., cytotoxic) agents of the invention that include a detectable label can be administered in a pharmaceutical compound to a subject (e.g., a cancer patient) or these compositions can be encoded by a vector (e.g., a viral vector) and expressed in a cell of the subject following administration.

An agent of the invention that incorporates a detectable label can be used, for example, to type, grade, and track the metastasis of a tumor in a subject having cancer. The diagnostic agent can also include a therapeutic agent (e.g., cytotoxic) of the invention. In this case, the diagnostic agent facilitates the detection or measurement, or binding to senescent cells, of the therapeutic agent after administration to a subject.

A diagnostic or therapeutic agent of the invention that includes a detectable label can be produced recombinantly in vitro. In one embodiment of the invention, the detectable label is capable of detection based on an intrinsic property, e.g., fluorescence and bioluminescence, or based on its ability to bind with another molecule capable of being detected (e.g., an epitope tag, such as c-myc, hemagglutinin, and histamine tags). Peptides, polypeptides, or proteins with diagnostic properties can be altered (e.g., by making amino acid substitutions, mutations, truncations, or additions) to facilitate incorporation into an agent of the invention. Desirable alterations include, for example, changes to the amino acid sequence that facilitate protein expression, longevity, cell secretion, and detectability.

The invention also features a nucleic acid molecule encoding a peptidic detectable label as a fusion protein with an agent of the invention; the nucleic acid molecule can be incorporated into a vector (e.g., an expression vector), such that, upon expression of the agent of the invention in a cell transfected or transduced with the vector, expression of the detectable label and agent of the invention are operably linked (e.g., fused, contiguously-joined, or tethered together).

Molecules that can be used as the detectable label as discussed herein include, but are not limited to, radioactive agents, fluorescent agents, bioluminescent molecules, epitope tags, and heavy metals, each of which is discussed in detail below.

Fluorescent agents include fluorochromes, such as fluorescein isothiocyanate (FITC), allophycocyanin (APC), phycoerythrin (PE), rhodamine, and tetramethyl rhodamine isothiocyanate (TRITC). Other fluorescent molecules include green fluorescent protein (GFP; SEQ ID NO: 27), enhanced GFP (eGFP), yellow fluorescent protein (SEQ ID NO: 28; YFP), cyan fluorescent protein (SEQ ID NO: 29; CFP), and red fluorescent protein (SEQ ID NO: 30; RFP or DsRed). Each of these fluorescent molecules can be used as detectable label in a diagnostic agent of the invention. Peptidic fluorescent molecules can be recombinantly expressed in a cell (e.g., a blood cell, such as a lymphocyte) following transfection or transduction of the cell with an expression vector that encodes the nucleotide sequence of the fluorescent molecule. Upon exposure of the fluorescent molecule to a stimulating frequency of light, the fluorescent molecule will emit light at a low, medium, or high intensity that can be observed by eye under a microscope or by an optical imaging device. Exemplary fluorescent molecules suitable for use as the detectable label in a diagnostic agent of the invention are described in, e.g., U.S. Pat. Nos. 7,417,131 and 7,413,874.

Bioluminescent molecules can also be used as a detectable label incorporated into a diagnostic agent of the invention. Bioluminescent molecules, such as luciferase (e.g., firefly (SEQ ID NO: 31), Renilla (SEQ ID NO: 32), and Omphalotus luciferase) and aequorin, emit light as part of a chemical reaction with a substrate (e.g., luciferin and coelenterazine). In one embodiment of the invention, a vector encoding a luciferase gene provides for the in vivo, in vitro, or ex vivo detection of cells (e.g., blood cells, such as lymphocytes) that have been transduced or transfected with an agent of the invention. Exemplary bioluminescent molecules suitable for use as the detectable label in a diagnostic agent of the invention, and methods for their use are described in, e.g., U.S. Pat. Nos. 5,292,658, 5,670,356, 6,171,809, and 7,183,092.

Epitope tags are short amino acid sequences, e.g., 5-20 amino acid residues in length, that can be incorporated into an agent of the invention as a detectable label to allow for detection once expressed in a cell, secreted from the cell, or bound to a target cell (e.g., a senescent cell). An agent of the invention that incorporates an epitope tag as a diagnostic agent can be detected by virtue of its interaction with an antibody, antibody fragment, or other binding molecule specific for the epitope tag. Nucleotide sequences encoding the epitope tag are produced either by cloning appropriate portions of natural genes or by synthesizing a polynucleotide that encodes the epitope tag. An antibody, antibody fragment, or other binding molecule that binds an epitope tag can directly incorporate its own detectable label (e.g., a fluorochrome, radiolabel, heavy metal, or enzyme such as horseradish peroxidase) or serve as a target for a secondary antibody, antibody fragment, or other binding molecule that incorporates such a label. Exemplary epitope tags that can be used as a detectable label include c-myc (SEQ ID NO: 24), hemagglutinin (HA; SEQ ID NO: 25), and histidine tag (His₆; SEQ ID NO: 26). Furthermore, fluorescent (e.g., GFP) and bioluminescent molecules, discussed above, can also serve as epitope tags, as antibodies, antibody fragments, and other binding molecules are commercially available for the detection of these moieties.

Agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can also be coupled to a chelating agent to form diagnostic agents of the invention. Diagnostic agents can be prepared by various methods depending upon the chelator chosen. A portion of an agent of the invention (e.g., a portion of a peptide, polypeptide, protein, small molecule, antibody, or antibody fragment) can be isolated from a natural source, recombinantly produced, or synthesized. The portion of an agent of the invention is most conveniently prepared by techniques generally established in the art of peptide synthesis, such as the solid-phase approach. Solid-phase synthesis involves the stepwise addition of amino acid residues to a growing peptide chain that is linked to an insoluble support or matrix, such as polystyrene. The C-terminus residue of the peptide is first anchored to a commercially available support with its amino group protected with an N-protecting agent such as a t-butyloxycarbonyl group (tBoc) or a fluorenylmethoxycarbonyl (FMOC) group. The amino-protecting group is removed with suitable deprotecting agents such as TFA in the case of tBOC or piperidine for FMOC and the next amino acid residue (in N-protected form) is added with a coupling agent such as dicyclocarbodiimide (DCC). Upon formation of a peptide bond, the reagents are washed from the support. After addition of the final residue, the agent is cleaved from the support with a suitable reagent, such as trifluoroacetic acid (TFA) or hydrogen fluoride (HF).

Agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) and chelator components can be coupled to form a conjugate by reacting the free amino group of the threonine residue of a peptide portion of an agent of the invention with an appropriate functional group of the chelator, such as a carboxyl group or activated ester. For example, a conjugate may incorporate the chelator ethylenediaminetetraacetic acid (EDTA), common in the art of coordination chemistry, when functionalized with a carboxyl substituent on the ethylene chain. Synthesis of EDTA derivatives of this type are reported in Arya et al., Bioconjugate Chemistry, 2:323, 1991), wherein the four coordinating carboxyl groups are each blocked with a t-butyl group while the carboxyl substituent on the ethylene chain is free to react with the amino group of a peptide portion of the agent of the invention, thereby forming a conjugate.

A conjugate may incorporate a metal chelator component that is peptidic, i.e., compatible with solid-phase peptide synthesis. In this case, the chelator may be coupled to the agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) in the same manner as EDTA described above or more conveniently the chelator and agent of the invention are synthesized in toto starting from the C-terminal residue of the agent and ending with the N-terminal residue of the chelator.

Conjugates may further incorporate a linking group component that serves to couple the agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) to the chelator while not adversely affecting either the targeting function of the agent or the metal binding function of the chelator. Suitable linking groups include amino acid chains and alkyl chains functionalized with reactive groups for coupling to both the agent and the chelator. An amino acid chain is the preferred linking group when the chelator is peptidic so that the conjugate can be synthesized in toto by solid-phase techniques.

An alkyl chain linking group may be incorporated in the conjugate by reacting the amino group of the threonine residue of a peptide portion of an agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) with a first functional group on the alkyl chain, such as a carboxyl group or an activated ester. Subsequently the chelator is attached to the alkyl chain to complete the formation of the conjugate by reacting a second functional group on the alkyl chain with an appropriate group on the chelator. The second functional group on the alkyl chain is selected from substituents that are reactive with a functional group on the chelator while not being reactive with the threonine residue of the agent. For example, when the chelator incorporates a functional group such as a carboxyl group or an activated ester, the second functional group of the alkyl chain linking group can be an amino group. It will be appreciated that formation of the conjugate may require protection and deprotection of the functional groups present in order to avoid formation of undesired products. Protection and deprotection are accomplished using protecting groups, reagents, and protocols common in the art of organic synthesis. Particularly, protection and deprotection techniques employed in solid phase peptide synthesis described above may be used.

An alternative chemical linking group to an alkyl chain is polyethylene glycol (PEG), which is functionalized in the same manner as the alkyl chain described above for incorporation in the conjugates. It will be appreciated that linking groups may alternatively be coupled first to the chelator and then to the agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells).

In accordance with one aspect of the invention, agent-chelator conjugates of the invention incorporate a diagnostically useful metal capable of forming a complex. Suitable metals include, e.g., radionuclides, such as technetium and rhenium in their various forms (e.g., ^(99 m)TcO³⁺, ^(99 m)TcO₂ ⁺, ReO³⁺, and ReO₂ ⁺). Incorporation of the metal within the conjugate can be achieved by various methods common in the art of coordination chemistry. When the metal is technetium-99 m, the following general procedure may be used to form a technetium complex. An agent-chelator conjugate solution is formed initially by dissolving the conjugate in aqueous alcohol such as ethanol. The solution is then degassed to remove oxygen then thiol-protecting groups are removed with a suitable reagent, for example, with sodium hydroxide, and then neutralized with an organic acid, such as acetic acid (pH 6.0-6.5). In the labeling step, a stoichiometric excess of sodium pertechnetate, obtained from a molybdenum generator, is added to a solution of the conjugate with an amount of a reducing agent such as stannous chloride sufficient to reduce technetium and heated. The labeled conjugate may be separated from contaminants ^(99 m)TcO₄ ⁻ and colloidal ^(99 m)TcO₂ chromatographically, for example, with a C-18 Sep Pak cartridge.

In an alternative method, labeling of the agent of the invention can be accomplished by a transchelation reaction. The technetium source is a solution of technetium complexed with labile ligands facilitating ligand exchange with the selected chelator. Suitable ligands for transchelation include tartarate, citrate, and heptagluconate. In this instance the preferred reducing reagent is sodium dithionite. It will be appreciated that the conjugate may be labeled using the techniques described above, or alternatively the chelator itself may be labeled and subsequently coupled to the agent of the invention to form the conjugate; a process referred to as the “prelabeled ligand” method.

Another approach for labeling agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) involves immobilizing the agent-chelator conjugate on a solid-phase support through a linkage that is cleaved upon metal chelation. This is achieved when the chelator is coupled to a functional group of the support by one of the complexing atoms. Preferably, a complexing sulfur atom is coupled to the support which is functionalized with a sulfur protecting group such as maleimide.

When labeled with a diagnostically useful metal, agent-chelator conjugates of the invention can be used to detect tissue at risk of developing cancer (e.g., lung cancer, breast cancer, colon cancer, and prostate cancer), age-related diseases (e.g., cardiovascular disease, cerebrovascular disease, or Alzheimer's disease), tobacco-related diseases (e.g., emphysema, aortic aneurysms, esophageal cancer, or squamous cell cancer of the head and neck), or other diseases and disorders relating to or caused by cellular senescence by procedures established in the art of diagnostic imaging. An agent labeled with a radionuclide metal, such as technetium-99 m, may be administered to a mammal (e.g., a human) by intravenous injection in a pharmaceutically acceptable solution such as isotonic saline, or by other methods described herein. The amount of a labeled agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) appropriate for administration is dependent upon the distribution profile of the chosen conjugate in the sense that a rapidly cleared agent may be administered at higher doses than one that clears less rapidly. Unit doses acceptable for imaging tissues that contain senescent cells are in the range of, e.g., 5-40 mCi for a 70 kg individual. In vivo distribution and localization can be tracked by standard techniques described herein at an appropriate time subsequent to administration; typically between 30 minutes and 180 minutes depending upon the rate of accumulation at the target site with respect to the rate of clearance at non-target tissue.

Therapeutic or Cytotoxic Agents Coupled to Agents of the Invention

Any of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be coupled to any known cytotoxic or therapeutic moiety. Examples include, e.g., antineoplastic agents such as: Acivicin; Aclarubicin; Acodazole Hydrochloride; Acronine; Adozelesin; Adriamycin; Aldesleukin; Altretamine; Ambomycin; A. metantrone Acetate; Aminoglutethimide; Amsacrine; Anastrozole; Anthramycin; Asparaginase; Asperlin; Azacitidine; Azetepa; Azotomycin; Batimastat; Benzodepa; Bicalutamide; Bisantrene Hydrochloride; Bisnafide Dimesylate; Bizelesin; Bleomycin Sulfate; Brequinar Sodium; Bropirimine; Busulfan; Cactinomycin; Calusterone; Camptothecin; Caracemide; Carbetimer; Carboplatin; Carmustine; Carubicin Hydrochloride; Carzelesin; Cedefingol; Chlorambucil; Cirolemycin; Cisplatin; Cladribine; Combretestatin A-4; Crisnatol Mesylate; Cyclophosphamide; Cytarabine; Dacarbazine; DACA (N-[2-(Dimethyl-amino)ethyl]acridine-4-carboxamide); Dactinomycin; Daunorubicin Hydrochloride; Daunomycin; Decitabine; Dexormaplatin; Dezaguanine; Dezaguanine Mesylate; Diaziquone; Docetaxel; Dolasatins; Doxorubicin; Doxorubicin Hydrochloride; Droloxifene; Droloxifene Citrate; Dromostanolone Propionate; Duazomycin; Edatrexate; Eflornithine Hydrochloride; Ellipticine; Elsamitrucin; Enloplatin; Enpromate; Epipropidine; Epirubicin Hydrochloride; Erbulozole; Esorubicin Hydrochloride; Estramustine; Estramustine Phosphate Sodium; Etanidazole; Ethiodized Oil 1131; Etoposide; Etoposide Phosphate; Etoprine; Fadrozole Hydrochloride; Fazarabine; Fenretinide; Floxuridine; Fludarabine Phosphate; Fluorouracil; 5-FdUMP; Flurocitabine; Fosquidone; Fostriecin Sodium; Gemcitabine; Gemcitabine Hydrochloride; Gold Au 198; Homocamptothecin; Hydroxyurea; Idarubicin Hydrochloride; Ifosfamide; Ilmofosine; Interferon Alfa-2a; Interferon Alfa-2b; Interferon Alfa-nl; Interferon Alfa-n3; Interferon Beta-I a; Interferon Gamma-I b; Iproplatin; Irinotecan Hydrochloride; Lanreotide Acetate; Letrozole; Leuprolide Acetate; Liarozole Hydrochloride; Lometrexol Sodium; Lomustine; Losoxantrone Hydrochloride; Masoprocol; Maytansine; Mechlorethamine Hydrochloride; Megestrol Acetate; Melengestrol Acetate; Melphalan; Menogaril; Mercaptopurine; Methotrexate; Methotrexate Sodium; Metoprine; Meturedepa; Mitindomide; Mitocarcin; Mitocromin; Mitogillin; Mitomalcin; Mitomycin; Mitosper; Mitotane; Mitoxantrone Hydrochloride; Mycophenolic Acid; Nocodazole; Nogalamycin; Ormaplatin; Oxisuran; Paclitaxel; Pegaspargase; Peliomycin; Pentamustine; PeploycinSulfate; Perfosfamide; Pipobroman; Piposulfan; Piroxantrone Hydrochloride; Plicamycin; Plomestane; Porfimer Sodium; Porfiromycin; Prednimustine; Procarbazine Hydrochloride; Puromycin; Puromycin Hydrochloride; Pyrazofurin; Rhizoxin; Rhizoxin D; Riboprine; Rogletimide; Safingol; Safingol Hydrochloride; Semustine; Simtrazene; Sparfosate Sodium; Sparsomycin; Spirogermanium Hydrochloride; Spiromustine; Spiroplatin; Streptonigrin; Streptozocin; Strontium Chloride Sr 89; Sulofenur; Talisomycin; Taxane; Taxoid; Tecogalan Sodium; Tegafur; Teloxantrone Hydrochloride; Temoporfin; Teniposide; Teroxirone; Testolactone; Thiamiprine; Thioguanine; Thiotepa; Thymitaq; Tiazofurin; Tirapazamine; Tomudex; TOP53; Topotecan Hydrochloride; Toremifene Citrate; Trestolone Acetate; Triciribine Phosphate; Trimetrexate; Trimetrexate Glucuronate; Triptorelin; Tubulozole Hydrochloride; Uracil Mustard; Uredepa; Vapreotide; Verteporfin; Vinblastine; Vinblastine Sulfate; Vincristine; Vincristine Sulfate; Vindesine; Vindesine Sulfate; Vinepidine Sulfate; Vinglycinate Sulfate; Vinleurosine Sulfate; Vinorelbine Tartrate; Vinrosidine Sulfate; Vinzolidine Sulfate; Vorozole; Zeniplatin; Zinostatin; Zorubicin Hydrochloride; 2-Chlorodeoxyadenosine; 2′ Deoxyformycin; 9-aminocamptothecin; raltitrexed; N-propargyl-5,8-dideazafolic acid; 2chloro-2′-arabino-fluoro-2′-deoxyadenosine; 2-chloro-2′-deoxyadenosine; anisomycin; trichostatin A; hPRL-G129R; CEP-751; linomide; sulfur mustard; nitrogen mustard (mechlor ethamine); cyclophosphamide; melphalan; chlorambucil; ifosfamide; busulfan; N-methyl-Nnitrosourea (MNU); N,N′-Bis(2-chloroethyl)-N-nitrosourea (BCNU); N-(2-chloroethyl)-N′ cyclohexyl-N-nitrosourea (CCNU); N-(2-chloroethyl)-N′-(trans-4-methylcyclohexyl-N-nitrosourea (MeCCNU); N-(2-chloroethyl)-N′-(diethyl) ethylphosphonate-N-nitrosourea (fotemustine); streptozotocin; diacarbazine (DTIC); mitozolomide; temozolomide; thiotepa; mitomycin C; AZQ; adozelesin; Cisplatin; Carboplatin; Ormaplatin; Oxaliplatin; C1-973; DWA 2114R; JM216; JM335; Bis (platinum); tomudex; azacitidine; cytarabine; gemcitabine; 6-Mercaptopurine; 6-Thioguanine; Hypoxanthine; teniposide 9-amino camptothecin; Topotecan; CPT-11; Doxorubicin; Daunomycin; Epirubicin; darubicin; mitoxantrone; losoxantrone; Dactinomycin (Actinomycin D); amsacrine; pyrazoloacridine; all-trans retinol; 14-hydroxy-retro-retinol; all-trans retinoic acid; N-(4-Hydroxyphenyl) retinamide; 13-cis retinoic acid; 3-Methyl TTNEB; 9-cis retinoic acid; fludarabine (2-F-ara-AMP); or 2-chlorodeoxyadenosine (2-Cda).

Other therapeutic compounds include, but are not limited to, 20-pi-1,25 dihydroxyvitamin D3; 5-ethynyluracil; abiraterone; aclarubicin; acylfulvene; adecypenol; adozelesin; aldesleukin; ALL-TK antagonists; altretamine; ambamustine; amidox; amifostine; aminolevulinic acid; amrubicin; amsacrine; anagrelide; anastrozole; andrographolide; angiogenesis inhibitors; antagonist D; antagonist G; antarelix; anti-dorsalizing morphogenetic protein-1; antiandrogen, prostatic carcinoma; antiestrogen; antineoplaston; antisense oligonucleotides; aphidicolin glycinate; apoptosis gene modulators; apoptosis regulators; apurinic acid; ara-CDP-DL-PTBA; argininedeaminase; asulacrine; atamestane; atrimustine; axinastatin 1; axinastatin 2; axinastatin 3; azasetron; azatoxin; azatyrosine; baccatin III derivatives; balanol; batimastat; BCR/ABL antagonists; benzochlorins; benzoylstaurosporine; beta lactam derivatives; beta-alethine; betaclamycin B; betulinic acid; bFGF inhibitor; bicalutamide; bisantrene; bisaziridinylspermine; bisnafide; bistratene A; bizelesin; breflate; bleomycin A2; bleomycin B2; bropirimine; budotitane; buthionine sulfoximine; calcipotriol; calphostin C; camptothecin derivatives (e.g., 10-hydroxy-camptothecin); canarypox IL-2; capecitabine; carboxamide-amino-triazole; carboxyamidotriazole; CaRest M3; CARN 700; cartilage derived inhibitor; carzelesin; casein kinase inhibitors (ICOS); castanospermine; cecropin B; cetrorelix; chlorins; chloroquinoxaline sulfonamide; cicaprost; cis-porphyrin; cladribine; clomifene analogues; clotrimazole; collismycin A; collismycin B; combretastatin A4; combretastatin analogue; conagenin; crambescidin 816; crisnatol; cryptophycin 8; cryptophycin A derivatives; curacin A; cyclopentanthraquinones; cycloplatam; cypemycin; cytarabine ocfosfate; cytolytic factor; cytostatin; dacliximab; decitabine; dehydrodidemnin B; 2′deoxycoformycin (DCF); deslorelin; dexifosfamide; dexrazoxane; dexverapamil; diaziquone; didemnin B; didox; diethylnorspermine; dihydro-5-azacytidine; dihydrotaxol, 9-; dioxamycin; diphenyl spiromustine; discodermolide; docosanol; dolasetron; doxifluridine; droloxifene; dronabinol; duocarmycin SA; ebselen; ecomustine; edelfosine; edrecolomab; eflornithine; elemene; emitefur; epirubicin; epothilones (A, R=H; B, R=Me); epithilones; epristeride; estramustine analogue; estrogen agonists; estrogen antagonists; etanidazole; etoposide; etoposide 4′-phosphate (etopofos); exemestane; fadrozole; fazarabine; fenretinide; filgrastim; finasteride; flavopiridol; flezelastine; fluasterone; fludarabine; fluorodaunorunicin hydrochloride; forfenimex; formestane; fostriecin; fotemustine; gadolinium texaphyrin; gallium nitrate; galocitabine; ganirelix; gelatinase inhibitors; gemcitabine; glutathione inhibitors; hepsulfam; heregulin; hexamethylene bisacetamide; homoharringtonine (HHT); hypericin; ibandronic acid; idarubicin; idoxifene; idramantone; ilmofosine; ilomastat; imidazoacridones; imiquimod; immunostimulant peptides; insulin-like growth factor-1 receptor inhibitor; interferon agonists; interferons; interleukins; iobenguane; iododoxorubicin; ipomeanol, 4-; irinotecan; iroplact; irsogladine; isobengazole; isohomohalicondrin B; itasetron; jasplakinolide; kahalalide F; lamellarin-N triacetate; lanreotide; leinamycin; lenograstim; lentinan sulfate; leptolstatin; letrozole; leukemia inhibiting factor; leukocyte alpha interferon; leuprolide+estrogen+progesterone; leuprorelin; levamisole; liarozole; linear polyamine analogue; lipophilic disaccharide peptide; lipophilic platinum compounds; lissoclinamide 7; lobaplatin; lombricine; lometrexol; lonidamine; losoxantrone; lovastatin; loxoribine; lurtotecan; lutetium texaphyrin; lysofylline; lytic peptides; maytansine; mannostatin A; marimastat; masoprocol; maspin; matrilysin inhibitors; matrix metalloproteinase inhibitors; menogaril; rnerbarone; meterelin; methioninase; metoclopramide; MIF inhibitor; ifepristone; miltefosine; mirimostim; mismatched double stranded RNA; mithracin; mitoguazone; mitolactol; mitomycin analogues; mitonafide; mitotoxin fibroblast growth factor-saporin; mitoxantrone; mofarotene; molgramostim; monoclonal antibody, human chorionic gonadotrophin; monophosphoryl lipid A+myobacterium cell wall sk; mopidamol; multiple drug resistance gene inhibitor; multiple tumor suppressor 1-based therapy; mustard anticancer agent; mycaperoxide B; mycobacterial cell wall extract; myriaporone; N-acetyldinaline; N-substituted benzamides; nafarelin; nagrestip; naloxone+pentazocine; napavin; naphterpin; nartograstim; nedaplatin; nemorubicin; neridronic acid; neutral endopeptidase; nilutamide; nisamycin; nitric oxide modulators; nitroxide antioxidant; nitrullyn; 06-benzylguanine; octreotide; okicenone; oligonucleotides; onapristone; ondansetron; ondansetron; oracin; oral cytokine inducer; ormaplatin; osaterone; oxaliplatin; oxaunomycin; paclitaxel analogues; paclitaxel derivatives; palauamine; palmitoylrhizoxin; pamidronic acid; panaxytriol; panomifene; parabactin; pazelliptine; pegaspargase; peldesine; pentosan polysulfate sodium; pentostatin; pentrozole; perflubron; perfosfamide; perillyl alcohol; phenazinomycin; phenylacetate; phosphatase inhibitors; picibanil; pilocarpine hydrochloride; pirarubicin; piritrexim; placetin A; placetin B; plasminogen activator inhibitor; platinum complex; platinum compounds; platinum-triamine complex; podophyllotoxin; porfimer sodium; porfiromycin; propyl bis-acridone; prostaglandin J2; proteasome inhibitors; protein A-based immune modulator; protein kinase C inhibitor; protein kinase C inhibitors, microalgal; protein tyrosine phosphatase inhibitors; purine nucleoside phosphorylase inhibitors; purpurins; pyrazoloacridine; pyridoxylated hemoglobin polyoxyethylene conjugate; raf antagonists; raltitrexed; ramosetron; ras farnesyl protein transferase inhibitors; ras inhibitors; ras-GAP inhibitor; retelliptine demethylated; rhenium Re 186 etidronate; rhizoxin; ribozymes; RII retinamide; rogletimide; rohitukine; romurtide; roquinimex; rubiginone B 1; ruboxyl; safingol; saintopin; SarCNU; sarcophytol A; sargramostim; Sdi 1 mimetics; semustine; senescence derived inhibitor 1; sense oligonucleotides; signal transduction inhibitors; signal transduction modulators; single chain antigen binding protein; sizofiran; sobuzoxane; sodium borocaptate; sodium phenylacetate; solverol; somatomedin binding protein; sonermin; sparfosic acid; spicamycin D; spiromustine; splenopentin; spongistatin 1; squalamine; stem cell inhibitor; stem-cell division inhibitors; stipiamide; stromelysin inhibitors; sulfinosine; superactive vasoactive intestinal peptide antagonist; suradista; suramin; swainsonine; synthetic glycosaminoglycans; tallimustine; tamoxifen methiodide; tauromustine; tazarotene; tecogalan sodium; tegafur; tellurapyrylium; telomerase inhibitors; temoporfin; temozolomide; teniposide; tetrachlorodecaoxide; tetrazomine; thaliblastine; thalidomide; thiocoraline; thrombopoietin; thrombopoietin mimetic; thymalfasin; thymopoietin receptor agonist; thymotrinan; thyroid stimulating hormone; tin ethyl etiopurpurin; tirapazamine; titanocene dichloride; topotecan; topsentin; toremifene; totipotent stem cell factor; translation inhibitors; tretinoin; triacetyluridine; triciribine; trimetrexate; triptorelin; tropisetron; turosteride; tyrosine kinase inhibitors; tyrphostins; UBC inhibitors; ubenimex; urogenital sinus-derived growth inhibitory factor; urokinase receptor antagonists; vapreotide; variolin B; vector system, erythrocyte gene therapy; velaresol; veramine; verdins; verteporfin; vinorelbine; vinxaltine; vitaxin; vorozole; zanoterone; zeniplatin; zilascorb; and zinostatin stimalamer.

One or more of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can also be coupled to a lytic peptide. Such lytic peptides induce cell death and include, but are not limited to, streptolysin O; stoichactis toxin; phallolysin; staphylococcus alpha toxin; holothurin A; digitonin; melittin; lysolecithin; cardiotoxin; and cerebratulus A toxin (Kern et al., J. Biol. Chem. 253(16):5752-5757, 1978). Agents of the invention can also be coupled to a synthetic peptide that shares some sequence homology or chemical characteristics with any of the naturally occurring peptide lysins; such characteristics include, but are not limited to, linearity, positive charge, amphipathicity, and formation of alpha-helical structures in a hydrophobic environment (Leuschner et al., Biology of Reproduction 73:860-865, 2005). Agents of the invention can also be coupled to an agent that induces complement-mediated cell lysis such as, for example, the immunoglobulin F_(c) subunit. Agents of the invention can also coupled to any member of the phospholipase family of enzymes (including phospholipase A, phospholipase B, phospholipase C, or phospholipase D) or to a catalytically-active subunit thereof.

Agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, or antibody fragments that target senescent cells) can also be coupled to a radioactive agent, including, but not limited to: Fibrinogen ¹²⁵I; Fludeoxyglucose ¹⁸F; Fluorodopa ¹⁸F; Insulin ¹²⁵I; Insulin ¹³¹I; lobenguane ¹²³I; Iodipamide Sodium ¹³¹I; Iodoantipyrine ¹³¹I; Iodocholesterol ¹³¹I; lodohippurate Sodium ¹²³I; Iodohippurate Sodium ¹²⁵I; Iodohippurate Sodium ¹³¹I; Iodopyracet ¹²⁵I; Iodopyracet ¹³¹I; lofetamine Hydrochloride ¹²³I; lomethin ¹²⁵I; Iomethin ¹³¹I; Iothalamate Sodium ¹²⁵I; Iothalamate Sodium ¹³¹I; tyrosine ¹³¹I; Liothyronine ¹²⁵I; Liothyronine ¹³¹I; Merisoprol Acetate ¹⁹⁷Hg; Merisoprol Acetate ²⁰³Hg; Merisoprol ¹⁹⁷Hg; Selenomethionine ⁷⁵Se; Technetium ^(99m)Tc Antimony Trisulfide Colloid; Technetium ^(99m)Tc Bicisate; Technetium ^(99m)Tc Disofenin; Technetium ^(99m)Tc Etidronate; Technetium ^(99m)Tc Exametazime; Technetium ^(99m)Tc Furifosmin; Technetium ^(99m)Tc Gluceptate; Technetium ^(99m)Tc Lidofenin; Technetium ^(99m)Tc Mebrofenin; Technetium ^(99m)Tc Medronate; Technetium ^(99m)Tc Medronate Disodium; Technetium ^(99m)Tc Mertiatide; Technetium ^(99m)Tc Oxidronate; Technetium ^(99m)Tc Pentetate; Technetium ^(99m)Tc Pentetate Calcium Trisodium; Technetium ^(99m)Tc Sestamibi; Technetium ^(99m)Tc Siboroxime; Technetium ^(99m)Tc; Succimer; Technetium ^(99m)Tc Sulfur Colloid; Technetium ^(99m)Tc Teboroxime; Technetium ^(99m)Tc Tetrofosmin; Technetium ^(99m)Tc Tiatide; Thyroxine ¹²⁵I; Thyroxine ¹³¹I; Tolpovidone ¹³¹I; Triolein ¹²⁵I; or Triolein ¹³¹I.

Therapeutic or cytotoxic agents may further include, for example, anti-cancer Supplementary Potentiating Agents, including, but not limited to: Tricyclic anti-depressant drugs (e.g., imipramine, desipramine, amitryptyline, clomipramine, trimipramine, doxepin, nortriptyline, protriptyline, amoxapine, and maprotiline); non-tricyclic anti-depressant drugs (e.g., sertraline, trazodone, and citalopram); Ca²⁺ antagonists (e.g., verapamil, nifedipine, nitrendipine, and caroverine); Calmodulin inhibitors (e.g., prenylamine, trifluoroperazine, and clomipramine); Amphotericin B; Triparanol analogs (e.g., tamoxifen); antiarrhythmic drugs (e.g., quinidine); antihypertensive drugs (e.g., reserpine); Thiol depleters (e.g., buthionine and sulfoximine) and Multiple Drug Resistance reducing agents such as Cremaphor EL.

The agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can also be administered with cytokines, such as granulocyte colony stimulating factor, or anticancer agents used in anti-cancer cocktails including, e.g., those shown with their MTDs in parentheses: gemcitabine (1000 mg/m²); methotrexate (15 gm/m² i.v.+leuco. <500 mg/m² i.v. w/o leuco); 5-FU (500 mg/m²/day×5 days); FUDR (100 mg/kg×5 in mice, 0.6 mg/kg/day in human i.a.); FdUMP; Hydroxyurea (35 mg/kg/d in man); Docetaxel (60-100 mg/m²); discodermolide; epothilones; vincristine (1.4 mg/m²); vinblastine (escalating: 3.3-11.1 mg/m², or rarely to 18.5 mg/m²); vinorelbine (30 mg/m²/wk); meta-pac; irinotecan (50-150 mg/m²,1×/wk depending on patient response); SN-38 (−100 times more potent than Irinotecan); 10-OH campto; topotecan (1.5 mg/m²/day in humans, 1×iv LD1Omice=75 mg/m²); etoposide (100 mg/m² in man); adriamycin; flavopiridol; Cis-Pt (100 mg/m² in man); carbo-Pt (360 mg/m² in man); bleomycin (20 mg/m2); mitomycin C (20 mg/m²); mithramycin (30 sug/kg); capecitabine (2.5 g/m² orally); cytarabine (100 mg/m²/day); 2-Cl-2′deoxyadenosine; Fludarabine-P04 (25 mg/m²/day, ×5 days); mitoxantrone (12-14 mg/m²); mitozolomide (>400 mg/m²); Pentostatin; or Tomudex.

Any of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be coupled to an antimetabolic agent. Antimetabolic agents include, but are not limited to, the following compounds and their derivatives: azathioprine, cladribine, cytarabine, dacarbazine, fludarabine phosphate, fluorouracil, gencitabine chlorhydrate, mercaptopurine, methotrexate, mitobronitol, mitotane, proguanil chlorohydrate, pyrimethamine, raltitrexed, trimetrexate glucuronate, urethane, vinblastine sulfate, vincristine sulfate, etc. In other embodiments, the agents of the invention can be coupled to a folic acid-type antimetabolite, a class of agents that includes, for example, methotrexate, proguanil chlorhydrate, pyrimethanime, trimethoprirne, or trimetrexate glucuronate, or derivatives of these compounds.

In another embodiment, any of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be coupled to a member of the anthracycline family of neoplastic agents, including but not limited to aclarubicine chlorhydrate, daunorubicine chlorhydrate, doxorubicine chlorhydrate, epirubicine chlorhydrate, idarubicine chlorhydrate, pirarubicine, or zorubicine chlorhydrate; a camptothecin, or its derivatives or related compounds, such as 10, 11 methylenedioxycamptothecin; or a member of the maytansinoid family of compounds, which includes a variety of structurally-related compounds, e.g., ansamitocin P3, maytansine, 2′-N-demethylmaytanbutine, and maytanbicyclinol.

Any of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be modified or labeled to facilitate diagnostic or therapeutic uses. Detectable labels such as a radioactive, fluorescent, heavy metal, or other agents may be bound to any of the agents of the invention. Single, dual, or multiple labeling of an agent may be advantageous. For example, dual labeling with radioactive iodination of one or more residues combined with the additional coupling of, for example, ⁹⁰Y via a chelating group to amine-containing side or reactive groups, would allow combination labeling. This may be useful for specialized diagnostic needs such as identification of widely dispersed small neoplastic cell masses.

Agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells), or analogs thereof, can also be modified, for example, by halogenation of the tyrosine residues of the peptide component. Halogens include fluorine, chlorine, bromine, iodine, and astatine. Such halogenated agents may be detectably labeled, e.g., if the halogen is a radioisotope, such as, for example, ¹⁸F, ⁷⁵Br, ⁷⁷Br, ¹²²I, ¹²³I, ¹²⁴I, ¹²⁵I, ¹²⁹I, ¹³¹I, or ²¹¹At. Halogenated agents of the invention contain a halogen covalently bound to at least one amino acid, and preferably to D-Tyr residues in each agent molecule. Other suitable detectable modifications include binding of other compounds (e.g., a fluorochrome such as fluorescein) to a lysine residue of the agent of the invention, or analog, particularly an agent or analog having a linker including lysines.

Radioisotopes for radiolabeling any of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) include any radioisotope that can be covalently bound to a residue of the peptide component of the agent of the invention or analog thereof. The radioisotopes can be selected from radioisotopes that emit either beta or gamma radiation, or alternatively, any of the agents of the invention can be modified to contain chelating groups that, for example, can be covalently bonded to lysine residue(s) of the analog. The chelating groups can then be modified to contain any of a variety of radioisotopes, such as gallium, indium, technetium, ytterbium, rhenium, or thallium (e.g., ¹²⁵I, ⁶⁷Ga, ¹¹¹In, ⁹⁹mTc, ¹⁶⁹Yb, ¹⁸⁶Re).

When one or more of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) is modified by attachment of a radioisotope, preferable radioisotopes are those having a radioactive half-life corresponding to, or longer than, the biological half-life of the agent used. More preferably, the radioisotope is a radioisotope of a halogen atom (e.g. a radioisotope of fluorine, chlorine, bromine, iodine, and astatine), even more preferably ⁷⁵Br, ⁷⁷Br, ⁷⁶Br, ¹²²I, ¹²³I, ¹²⁴I, ¹²⁵I, ¹²⁹I, ¹³¹I, or ²¹¹At.

Agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) coupled to radioactive metals are useful in radiographic imaging or radiotherapy. Preferred radioisotopes also include ^(99m)Tc, ⁵¹Cr, ⁶⁷Ga, ⁶⁸Ga, ¹¹¹In, ¹⁶⁸Yb, ¹⁴⁰La, ⁹⁰Y, ⁸⁸Y, ¹⁵³Sm, ¹⁵⁶Ho, ¹⁶⁵Dy, ⁶⁴Cu, ⁹⁷Ru, ¹⁰³Ru, ¹⁸⁶Re, ¹⁸⁸Re, ²⁰³Pb, ²¹¹Bi, ²¹²Bi, ²¹³Bi, and ²¹⁴Bi. The choice of metal can be determined based on the desired therapeutic or diagnostic application.

The agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells), when coupled to a metal component, are useful as diagnostic and/or therapeutic agents. A detectable label may be a metal ion from heavy elements or rare earth ions, such as Gd³⁺, Fe³⁺, Mn³⁺, or Cr²⁺. Conjugates that include paramagnetic or superparamagnetic metals are useful as diagnostic agents in MRI imaging applications. Paramagnetic metals that can be coupled to the agents of the invention include, but are not limited to, chromium (III), manganese (II), iron (II), iron (III), cobalt (II), nickel (II), copper (II), praseodymium (III), neodymium (III), samarium (III), gadolinium (III), terbium (III), dysprosium (III), holmium (III), erbium (III), and ytterbium (III). Preferably, the polymer has a relaxtivity of at least 10, 12, 15, or 20 mM⁻¹ sec⁻¹ Z⁻¹, wherein Z is the concentration of paramagnetic metal.

Chelating groups may be used to indirectly couple detectable labels or other molecules to an agents of the invention (e.g., a peptide, polypeptide, protein, small molecule, antibody, or antibody fragment). Chelating groups can link agents of the invention with radiolabels, such as a bifunctional stable chelator, or can be linked to one or more terminal or internal amino acid reactive groups. Conjugates can be linked via an isothiocyanate β-Ala or appropriate non α-amino acid linker which prevents Edman degradation. Examples of chelators known in the art include, for example, the ininocarboxylic and polyaminopolycarboxylic reactive groups, ininocarboxylic and polyaminopolycarboxylic reactive groups, diethylenetriaminepentaacetic acid (DTPA), and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA).

An agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can also be coupled directly to a cytotoxic or therapeutic agent using known chemical methods, or the two moieties can be coupled via an indirect linkage, such as through a chelating group. For example, the agent can be attached to a chelating group that is attached to the cytotoxic or therapeutic agent. Chelating groups include, but are not limited to, ininocarboxylic and polyaminopolycarboxylic reactive groups, diethylenetriaminepentaacetic acid (DTPA), and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). For general methods, see, e.g., Liu et al., Bioconjugate Chem. 12(4):653, 2001; Cheng et al., WO 89/12631; Kieffer et al., WO 93/12112; Albert et al., U.S. Pat. No. 5,753,627; and WO 91/01144 (each of which are hereby incorporated by reference).

When coupled to a therapeutic or cytotoxic agent, specific targeting by the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) allows selective destruction of senescent cells. For example, the agents of the invention can be used to target and destroy senescent cells of the lung, breast, prostate, and colon in order to prevent, stabilize, inhibit the progression of, or treat cancers originating in these organs. Also, for example, the agents of the invention can be used to target and destroy senescent cells of the vasculature, brain, liver, kidney, heart, lung, prostate, colon, nasopharynx, oropharynx, larynx, bronchus, and skin in order to prevent, stabilize, inhibit the progression of, or treat age-related diseases or tobacco-related diseases or conditions relating to these organs. Any of the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be administered to a mammalian subject, such as a human, directly or in combination with any pharmaceutically acceptable carrier or salt known in the art. Pharmaceutically acceptable salts may include non-toxic acid addition salts or metal complexes that are commonly used in the pharmaceutical industry. Examples of acid addition salts include organic acids such as acetic, lactic, pamoic, maleic, citric, malic, ascorbic, succinic, benzoic, palmitic, suberic, salicylic, tartaric, methanesulfonic, toluenesulfonic, or trifluoroacetic acids or the like; polymeric acids such as tannic acid, carboxymethyl cellulose, or the like; and inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid phosphoric acid, or the like. Metal complexes include zinc, iron, and the like. One exemplary pharmaceutically acceptable carrier is physiological saline. Other physiologically acceptable carriers and their formulations are known to one skilled in the art and described, for example, in Remington's Pharmaceutical Sciences, (18^(th) edition), ed. A. Gennaro, 1990, Mack Publishing Company, Easton, Pa.

Agents of the Invention for Use in Cellular Therapy Applications

One or more agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) can be used to improve the efficacy of a cellular therapy provided to a patient (e.g., a mammal, such as a human) in need thereof by depleting (i.e., killing) one or more, all, or substantially all (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99% or more) senescent cells in the transferred donor cells, tissue, or organ prior to, concurrent with, or following administration of the cellular therapy. Alternatively, a patient (e.g., a mammal, such as a human) may be treated with one or more agents of the invention prior to, concurrent with, or following administration of the cellular therapy. Cellular therapies include, without limitation, the autologous, allogeneic, syngeneic, or xenogeneic transplantation or engraftment of cells (e.g., blood, pancreatic islet cells, and stem cells (e.g., hematopoietic stem cells (HSC), umbilical cord blood stem cells (see, e.g., US Patent Application Publication 2002/0164794), pluripotent stem cells (e.g., hox11-expressing pluripotent stem cells described in US Patent Application Publication 2005/0158288), multipotent stem cells, and totipotent stem cells), tissues (e.g., skin and adipose tissue), or organs (e.g., kidney, liver, heart, and lung) to a patient (e.g., a mammal, such as a human) in need thereof. Cellular therapies (e.g., cell (e.g., stem cells), tissue, or organ transplantation or engraftment) are currently being developed for a wide range of therapeutic indications for degenerative and pathologic diseases, such as osteoarthritis (see, e.g., U.S. Patent Application Publication No. 2007/0264238), ischemia and cardiac tissue damage, such as that caused by myocardial infarction (see, e.g., Dzau et al., U.S. Patent Application Publication No. 2007/0259425), type I and type II diabetes (see, e.g., Uchida et al., U.S. Patent Application Publication No. 2007/0212732), renal dysfunction and multi-organ failure (see, e.g., Westenfelder, U.S. Patent Application Publication No. 2007/0178071), and neurodegenerative diseases (see, e.g., Kim et al., U.S. Patent Application Publication No. 2007/0054399). The preceding U.S. patent application Publications are hereby incorporated by reference in their entirety.

Administration and Dosages

Pharmaceutical formulations of a therapeutically effective amount of an agent of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells), or pharmaceutically acceptable salt-thereof, can be administered orally, parenterally (e.g., intramuscular, intraperitoneal, intravenous, or subcutaneous injection, inhalation, intradermally, optical drops, or implant), nasally, vaginally, rectally, sublingually, or topically. The pharmaceutical formulation can include the agent of the invention in admixture with a pharmaceutically acceptable carrier adapted for the route of administration.

Methods well known in the art for making pharmaceutical formulations can be found, for example, in Remington's Pharmaceutical Sciences (18^(th) edition), ed. A. Gennaro, 1990, Mack Publishing Company, Easton, Pa. Compositions intended for oral use may be prepared in solid or liquid forms according to any method known to the art for the manufacture of pharmaceutical compositions. The compositions may optionally contain sweetening, flavoring, coloring, perfuming, and/or preserving agents in order to provide a more palatable preparation. Solid dosage forms for oral administration include capsules, tablets, pills, powders, and granules. In such solid forms, the active compound is admixed with at least one inert pharmaceutically acceptable carrier or excipient. These may include, for example, inert diluents, such as calcium carbonate, sodium carbonate, lactose, sucrose, starch, calcium phosphate, sodium phosphate, or kaolin. Binding agents, buffering agents, and/or lubricating agents (e.g., magnesium stearate) may also be used. Tablets and pills can additionally be prepared with enteric coatings.

Liquid dosage forms for oral administration include pharmaceutically acceptable emulsions, solutions, suspensions, syrups, and soft gelatin capsules. These forms contain inert diluents commonly used in the art, such as water or an oil medium. Besides such inert diluents, compositions can also include adjuvants, such as wetting agents, emulsifying agents, and suspending agents.

Formulations for parenteral administration include sterile aqueous or non-aqueous solutions, suspensions, or emulsions. Examples of suitable vehicles include propylene glycol, polyethylene glycol, vegetable oils, gelatin, hydrogenated naphthalenes, and injectable organic esters, such as ethyl oleate. Such formulations may also contain adjuvants, such as preserving, wetting, emulsifying, and dispersing agents. Biocompatible, biodegradable lactide polymer, lactide/glycolide copolymer, or polyoxyethylene-polyoxypropylene copolymers may be used to control the release of the compounds. Other potentially useful parenteral delivery systems for the agents of the invention include ethylene-vinyl acetate copolymer particles, osmotic pumps, implantable infusion systems, and liposomes.

Liquid formulations can be sterilized by, for example, filtration through a bacteria-retaining filter, by incorporating sterilizing agents into the compositions, or by irradiating or heating the compositions. Alternatively, they can also be manufactured in the form of sterile, solid compositions which can be dissolved in sterile water or some other sterile injectable medium immediately before use.

Compositions for rectal or vaginal administration are preferably suppositories which may contain, in addition to active substances, excipients such as coca butter or a suppository wax. Compositions for nasal or sublingual administration are also prepared with standard excipients known in the art. Formulations for inhalation may contain excipients, for example, lactose, or may be aqueous solutions containing, for example, polyoxyethylene-9-lauryl ether, glycocholate and deoxycholate, or may be oily solutions for administration in the form of nasal drops or spray, or as a gel.

The amount of active ingredient in the compositions of the invention can be varied. One skilled in the art will appreciate that the exact individual dosages may be adjusted somewhat depending upon a variety of factors, including the agent being administered, the time of administration, the route of administration, the nature of the formulation, the rate of excretion, the nature of the subject's conditions, and the age, weight, health, and gender of the patient. In addition, the severity of the condition targeted by an agent of the invention will also have an impact on the dosage level. Generally, dosage levels of an agent of the invention of between 0.1 μg/kg to 100 mg/kg of body weight are administered daily as a single dose or divided into multiple doses. Preferably, the general dosage range is between 250 μg/kg to 5.0 mg/kg of body weight per day. Wide variations in the needed dosage are to be expected in view of the differing efficiencies of the various routes of administration. For instance, oral administration generally would be expected to require higher dosage levels than administration by intravenous injection. Variations in these dosage levels can be adjusted using standard empirical routines for optimization, which are well known in the art. In general, the precise therapeutically effective dosage can be determined by the attending physician in consideration of the above-identified factors.

An agent of the invention (e.g., a peptide, polypeptide, protein, small molecule, antibody, or antibody fragment that targets senescent cells) can be administered in a sustained release composition, such as those described in, for example, U.S. Pat. Nos. 5,672,659, 5,595,760. The use of immediate or sustained release compositions depends on the type of condition being treated. If the condition consists of an acute or over-acute disorder, a treatment with an immediate release form will be preferred over a prolonged release composition. Alternatively, for preventative or long-term treatments, a sustained released composition will generally be preferred.

An agent of the invention (e.g., a peptide, polypeptide, protein, small molecule, antibody, or antibody fragment that targets senescent cells) can be prepared in any suitable manner. The agent may be isolated from naturally-occurring sources, recombinantly produced, or produced synthetically, identified from a library of small molecules, or produced by a combination of these methods. The synthesis of short peptides is well known in the art. See e.g., Stewart et al., Solid Phase Peptide Synthesis (Pierce Chemical Co., 2d ed., 1984). A peptide portion of any of the agents of the invention can be synthesized according to standard peptide synthesis methods known in the art.

The present invention is illustrated by the following examples, which are in no way intended to be limiting of the invention.

EXAMPLES Example 1 Discovery of Agents that Bind Senescent Cells

Phage Selection Technique

Normal skin cell line CCD-1070Sk was obtained from American Type Culture Collection (Bethesda, Md.). The cells were grown in Eagle's Minimal Essential medium with Earle's BSS, 2 mM L-glutamine, 1.0 mM Sodium pyruvate, 0.1 mM nonessential amino acids and 1.5 g/L sodium bicarbonate supplemented with 10% fetal bovine serum.

Cells were sub-cultured every 4-5 days till they became senescent. Cell senescence was confirmed by senescence-associated beta-galactosidase staining.

An M13 phage peptide library, Ph.D.-12, was obtained from New England BioLabs (Beverly, Mass.), which displays random 12-mer peptides.

For the selection step for round 1, an aliquot (10 μL) of the Ph.D.-12 complete phage library was incubated with 5×10⁵ cells of senescent fibroblasts in 1 mL PBS/0.5% BSA for ˜3.5 hours at room temperature with slow shaking on Lab-Quake. At the end of the incubation, the cells were pelleted in a microcentrifuge at 1500 RPM for 2 minutes and the supernatant removed. Cells were washed with PBS/1.0% BSA/0.5% Tween (wash buffer) for a total of 4 washes using fresh tubes between washes. Phage that bound to the target cells were eluted with 200 μL of 0.2 M glycine (pH 2.2) for 8 minutes then neutralized with 30 μL of 1 M Tris-HCl (pH 9.0). The number of phage bound was determined and the remaining eluate was amplified.

From the amplified eluate from Round 1, an aliquot (2×10¹¹ phage) was used for subtraction panning against normal skin fibroblasts. The phage were incubated with 2×10⁶ cells of normal skin fibroblast (CC D 1070 sk) at room temperature for 60 minutes at room temperature with slow shaking in PBS with 0.5% BSA. At the end of incubation, the cells were pelleted in a microcentrifuge at 1500 RPM for 2 minutes and the supernatant recovered. The supernatant was used to resuspend another 2×10⁶ subtraction cells. This subtraction step was repeated 3 times for each round.

After the final subtraction step in each round, the recovered phage supernatant was used to suspend 5×10⁵ selection cells. The bound phage were recovered and amplified as described above. The process was repeated for a total of 5 rounds of selection. After the fifth round of selection, phage were titered and 20 well-separated plaques were picked, amplified, and sequenced.

Results:

Three consensus sequences were obtained from the phage display selection procedure. These correspond to the SEQ ID NOS:1-3. SEQ ID NO:1 represented 9/20 clones, SEQ ID NO:2 represented 6/20 clones, and SEQ ID NO:3 represented 2/20 clones.

Example 2 Human Study to Test the Prognostic Use of a Senescent Cell Binding Agent Labeled with a Radioisotope; Using a Senescent Cell Detecting Radiotracer to Predict Cancer Risk

This study is designed to show that noninvasive, in vivo imaging of senescent cell content can be used to predict cancer risk in smokers. Six-hundred subjects will be enrolled. Eighty percent of these subjects will be smokers; twenty percent will be nonsmokers. Subjects less than 18 years of age, subjects with a history of cancer, and pregnant subjects will be excluded. The anticipated mean age of study subjects is 55 years. Each study subject will undergo scintigraphic imaging using a radio-labeled peptide of the invention (SEQ ID NO:1) as the radiopharmaceutical. The radiopharmaceutical will be prepared by reacting peptide-gly-gly-gly-ser-DTPA with 111-In chloride. Each study subject will receive an intravenously administered dose of 5 mCi of 111-In labeled peptide. Anterior and posterior whole body planar images of the subjects will be obtained at 24 and 48 hours following administration of the radio-labeled peptide. SPECT imaging of the chest will also be obtained at 24 and 48 hours following administration of the radio-labeled peptide. Scintigraphic images will be acquired on a SPECT/CT camera using a medium energy collimator. Two radiologists will read the SPECT/CT study of each subject. Regions of interest will be drawn around each lung and the mediastinum. The activity within each region will be determined for each subject. Subjects will be followed for two years and monitored for the incidence of lung cancer. Kaplan-Meier curves will be drawn for the study population based upon cancer free survival. An optimal threshold of activity within the regions of interest will be determined such as to divide subjects that develop cancer from subjects who don't; a Kaplan-Meier curve will be drawn for the set of subjects with activity levels above the threshold and a Kaplan-Meier curve will be drawn for subjects with activity levels below the threshold level. We expect to observe development of lung cancer in approximately twenty subjects. Activity in pulmonary regions of interest will be significantly higher in smokers than nonsmokers. Smokers who develop lung cancer will have significantly higher activity in pulmonary regions of interest than smokers who do not develop lung cancer. Cancer-free survival curves will be significantly different for subjects with a pulmonary region of interest activity level above the threshold value than for subjects with activities below the threshold value.

Example 3 Using Senescent Cell Binding Agents Coupled to Cytotoxic Agents to Eliminate Senescent Cells: Effect on Subsequent Development of Cancer

The purpose of this study is to show that elimination of some senescent cells from an organism using the agents of the invention (e.g., peptides, polypeptides, proteins, small molecules, antibodies, or antibody fragments that target senescent cells) will reduce the risk of subsequently developing cancer. For example, a senescent cell binding peptide. (SEQ ID NO:1) will be conjugated to a cytotoxic peptide having the sequence KFAKFAKKFAKFAKKFAKFAK (SEQ ID NO:4; Leuschner and Hansel, Biology of Reproduction 73:860-865) via an amino acid linker sequence (e.g., a linker sequence selected from GGGC (SEQ ID NO:9), GGGS (SEQ ID NO:10), and GG) at the C terminus of the senescent cell binding peptide. Study subjects will consist of 60 BALB/c mice, mean age 6 mo which includes 30 experimental animals and 30 controls. Experimental animals will receive an intravenously administered dose of 0.2 mg/Kg of body weight of senescent cell binding peptide conjugate once every three months for one year. Control animals will receive an equal dose of a 37 amino acid control peptide. Kaplan-Meier curves representing tumor free survival will be constructed for each group of mice. Approximately 30% of control mice will develop tumors by the end of the study period. The study is expected to show significantly longer tumor free survival in the experimental group compared to the control group.

Example 4 Reduction of Senescent Cell Content in Diabetic Mice by Treatment with a Senescent Cell Cytotoxic Agent

Diabetes is induced in female CD-1 mice, 5-7 weeks old and 25-35 g in body weight, by intraperitoneal injection of 200 mg/Kg body weight of streptozotocin dissolved in sodium citrate saline buffer (pH 4.5). Tail vein blood glucose will be measured 5 days after injection to ensure induction of diabetes. Diabetic mice will be maintained at constant temperature (23° C.) with 12 hour light and 12 hour dark cycles for 16 weeks following confirmation of diabetes. Seven diabetic mice will receive a weekly tail vein injection of a senescent cell cytotoxic agent (SenL; SEQ ID NO:6; GVYHFAPLTPTPGGGSKFAKFAKKFAKFAK; 300 μg/dose), comprising a senescent cell binding sequence linked to a lytic peptide sequence during the 16 weeks. Seven control animals will receive an equivalent volume TV injection of normal saline. At the end of 16 weeks, all animals will be sacrificed. Tissue cross sections will be prepared from aorta, lung, liver, and heart from snap frozen tissue. Tissue samples will be stained for SA-β-gal activity using the method of Campisi et al. Percentage of SA-β-gal positive cells will be determined for each tissue sample from each animal by counting 1000 cells in each of four random microscopic fields for each tissue sample. A two-tailed I-test will be used to evaluate the loss of senescent cells in the tissues of diabetic mice treated with senescent cell cytotoxic agent relative to the loss of senescent cells in the tissues of diabetic control mice.

Example 5 Enhancement of Stem Cell Treatments by Pre-Treatment with Senescent Cell Binding Agents Coupled to Cytotoxic Agents: Effects on Subsequent Stem Cell Engraftment

The following experiment can be used to show that exogenously administered stem cells engraft at higher rates into damaged tissue if the treated organism undergoes pretreatment with a senescent cell cytotoxic agent of the invention (e.g., a peptide agent) to reduce the content of senescent cells in the damaged tissue compartment. Removal of senescent cells increases the engraftment of stem cells into damaged tissue.

Balb-C mice will undergo left anterior descending (LAD) artery ligation for 60 minutes to induce myocardial infarction. The mice will be pre-anesthetized in an isoflurane inhalation chamber and receive an i.p. injection of sodium pentobarbital (25 mg/kg). The animals will be intubated and ventilated for the duration of the procedure. The LAD artery will be identified following left lateral thoracotomy and pericardectomy. Ligation will be performed on the proximal 2 mm portion of the LAD using a 9-0 ethilon stitch. Mice will be maintained at 23° C. with 12 hour light and 12 hour dark cycles for 6 days. Seven surviving mice will be used as experimental animals and seven will be used as control animals. Experimental mice will receive tail vein injections of a senescent cell cytotoxic agent conjugated to a lytic peptide sequence (SEQ ID NO:8; GVYHFAPLTPTPGGKFAKFAKKFAKFAK; 300 μg/dose) every second day for six days.

Murine hematopoietic stem cells (HSC) will be obtained from StemCell Technologies Inc. Cells will be transfected to express enhanced green fluorescent protein (EGFP). Plasmid pEF-1 a-EGFP, containing an EGFP gene under the control of human EF1, a promoter, and a neomycin-resistance cassette, will be constructed as follows: (1) the promoter region of pEGFP-N3 (Clontech, Palo Alto, Calif.) will be removed by cutting out the AseI-NheI DNA fragment and joining the blunt-ended termini, and (2) human EF1, a promoter from pEF-BOS (a fragment of HindIII and EcoRI DNA) will be inserted into the HindII-EcoRI site of the plasmid. Murine HSC will be transfected with pEF-1 a-EGFP by electroporation and selected in the presence of G418. A single clone that brightly expresses EGFP will be chosen and used for the experiments. The clone will be adapted to feeder-free conditions and maintained on gelatin-coated dishes in Dulbecco's Modified Eagle's Media supplemented with 15% fetal calf serum, 2 mM sodium pyruvate, 2 mM L-glutamine, lx nonessential amino acids, 1,000 units of 0.1 mM 2-mercaptoethanol per mL, along with 100 units of streptomycin and 100 μg of penicillin per mL. Cells will be collected after trypsinization with EDTA and placed in aliquots of the medium described above for mouse tail vein injection 1 hour later.

HSC (10⁶) will be injected via tail vein into each experimental and control mouse. Ten days later, each animal will be sacrificed. Hearts will be excised and fixed in 2% paraformaldehyde in phosphate-buffered solution (PBS) for 2 hours and cryoprotected in 30% sucrose overnight. Tissue will be embedded in optimum cutting temperature medium and sectioned at 5 μm on a cryostat. Serial sections will be stained with hematoxylin and eosin (H&E). Tissue will be examined with a fluorescent microscope. Percentage of GFP positive cells will be determined for each cardiac tissue sample from each animal by counting 1000 cells in each of four random microscopic fields for each tissue sample. A two-tailed t-test will be used to evaluate the hypothesis that exogenously administered HSC engraft at a higher rate into mice treated with senescent cell cytotoxic agent relative to untreated controls. Special attention will be paid to cardiac tissue in the LAD territory (anterior wall) of each heart.

Example 6 In Vitro Validation of the Use of Senescent Cell Binding Agents as Agents to Deliver Molecular Cargo to the Cytoplasm of Senescent Cells

Cytotoxicity of Senescent Cell Binding Peptide Conjugated to a Lytic Peptide Sequence

Cytotoxic peptide SenL (i.e., SEQ ID NO:6) was synthesized by conjugating a senescent cell binding agent (SEQ ID NO:1) to a lytic peptide sequence (KFAKFAKKFAKFAK; SEQ ID NO:4) via a 4 residue linker (GGGS; SEQ ID NO:10) and tested for differential cytotoxic activity in senescent fibroblasts, prostate epithelial cells, and non-senescent fibroblasts. Senescent fibroblasts exhibited dose-dependent cell death at a significantly higher rate than either non-senescent fibroblasts or prostate epithelial cells (FIG. 1). The effect of SenL on cell proliferation was also assessed using the Cell Proliferation Assay WST-1 (Roche, Mannheim, Germany). As shown in FIG. 2, no change in cell proliferation was seen in any of the three cell types in response to treatment with SenL. The proliferation assay uses WST-1 as a reagent; the reaction is catalyzed by mitochondrial dehydrogenases. Senescent cells have higher mitochondrial mass than their non-senescent counterparts (Lee et al., J. Biomed. Sci. 9:517-26, 2002); consequently, baseline WST assay values are higher for senescent cells. The occurrence of cell death in response to treatment with SenL and absence of change in proliferation rate indicate that SenL causes cell death in non-proliferating cells, e.g. senescent cells.

It is worth noting that each cultured cell population contains a mixture of senescent and non-senescent cells at all population doublings, but that the relative proportion of senescent cells within the population increases stochastically with each population doubling (Martin-Ruiz et al., J. Biol. Chem. 279(17):17826-33, 2004). Thus, the “senescent cells” used in this cell killing experiment are predicted to contain a subpopulation of non-senescent cells. Likewise, a fraction of the “non-senescent cells” used in this experiment are predicted to be senescent. Therefore, the observed difference in cell killing between the two populations is reduced by the impure composition of each population with regard to senescence. This explains why some cytotoxicity is observed in the “non-senescent” fibroblast population. It also explains why the prostate epithelial cells (RWPE-1), which are not predicted to have any senescent cells due to immortalization through HPV-18 transduction, show no cell death at all.

In Vitro Cytotoxicity: Conjugation to Ricin-A

A senescent cell binding agent (i.e., SEQ ID NO:1) was conjugated to the ricin A subunit via a 4 peptide linker (GGGC; SEQ ID NO:9) to produce SenR (SEQ ID NO:7). Senescent fibroblasts, non-senescent fibroblasts, and prostate epithelial cells were then incubated with the peptide-ricin A conjugate (SenR). Increased cell death was observed in the case of senescent cells treated with SenR than in the other cell types (FIG. 3). For example, an approximately 3 fold increase in cell death was measured in senescent fibroblast when compared to non-senescent fibroblast when treated with 50 μM of SenR.

Binding of Peptide to Senescent Cells Versus Non-Senescent Cells

In the absence of unlabeled peptide, radio-labeled SenC bound to prostate epithelium, normal fibroblasts, and senescent cells at an average of 0.06%, 0.08%, and 0.32% of added dose, respectively, demonstrating that SenC binds to senescent cells at a higher rate than to the other cell types (P=0.001). In the presence of 20 μM unlabeled SenC, labeled SenC bound to prostate epithelium, normal fibroblasts, and senescent cells at an average of 0.06%, 0.09%, and 0.25% of added dose, respectively. There was no significant difference between binding rates in the presence or absence of unlabeled SenC in the case of prostate epithelium and normal fibroblasts (P=0.5 and 0.4 respectively), indicating that the binding to these cell types is nonspecific. Labeled SenC did bind at significantly different rates to senescent cells in the absence vs. presence of unlabeled SenC (P=0.04), indicative of specific binding (see FIG. 4).

Example 7 Isolation and Identification of Senescent Cell-Specific Antigens

Fibroblasts (CCD-1070Sk) were cultured as outlined above and divided into three groups: replicatively senescent, stress induced prematurely senescent, and non-senescent. Cell surface proteins of each group of cells were conjugated to biotin using the Pierce Cell Surface Protein Isolation Kit (Thermo Scientific, product number 89881) following the instructions of the manufacturer. Membrane proteins were captured using neutravidin following membrane dissolution and sent for 2D gel electrophoresis. Spots from each gel were analyzed to look for differences in protein expression among the three groups of fibroblasts. Protein spots occurring in the gels corresponding to senescent (replicative or stress-induced) cells but not in gels corresponding to non-senescent fibroblasts were identified as senescence-specific antigens and identified using MALDI-TOF mass spectrometry.

Mutant beta-actin (SEQ ID NO:11; GI: 28336) and ACTB protein (SEQ ID NO:12; GI: 15277503) were identified as cell-surface, senescence specific antigens occurring in both replicatively senescent and stress-induced prematurely senescent cells. Drug resistance-related protein LRP (SEQ ID NO:13; GI: 1097308) and major vault protein (SEQ ID NO:14; GI: 19913410) were identified as senescence-specific surface proteins in the replicatively senescent cells only. Senescence specific antigens that were identified in stress induced prematurely senescent cells included thyroid hormone binding protein precursor (SEQ ID NO:15; GI: 339647); unnamed protein product (SEQ ID NO:20; GI: 35655); prolyl 4-hydroxylase, beta subunit precursor (SEQ ID NO:16; GI: 20070125); chain A, human protein disulfide isomerase (SEQ ID NO:17; GI: 159162689); electron-transfer-flavoprotein, beta polypeptide (SEQ ID NO:18; GI: 4503609); unnamed protein product (SEQ ID NO:21; GI: 158257194); unnamed protein product (SEQ ID NO:22; GI: 158259937); ATP synthase, H⁺ transporting, mitochondrial F1 complex, alpha subunit precursor (SEQ ID NO:19; GI: 4757810), and cathepsin B (SEQ ID NO:23).

Methods

Induction of Replicative Senescence

CCD-1070Sk (fibroblasts) was cultured as described herein. Cells were cultured until they underwent 68 population doublings at which time they displayed typical senescent morphology and underwent minimal further cell growth in response to mitogens.

Isolation of Cell Surface Proteins

Cell surface proteins were extracted from three groups of cells (replicatively senescent fibroblasts, stress-induced prematurely senescent fibroblasts, and non-senescent fibroblasts). Each group of cells contained 10⁹ cells. Cell surface proteins were isolated using the Pierce Cell Surface Protein Isolation Kit (Thermo Scientific, product number 89881), following the instructions of the manufacturer. Protein isolates were analyzed using spectrophotometry which showed absorbances at 280 nm of 1.25, 1.375, and 1.347 for replicatively senescent cells, stress induced prematurely senescent cells, and non-senescent cells respectively. Total volume of each protein isolate was 500 μL.

Identification of Cell Surface Proteins

Cell surface protein isolates were sent for analysis by the proteomics core at the University of Massachusetts Medical School (Worcester, Mass.). The analysis was carried out by performing a buffer exchange for each protein isolate sample followed by 2D gel electrophoresis. Each gel was compared to find protein spots that occurred in the gels corresponding to the senescent (replicative or stress-induced) cells but not in the gels corresponding to the non-senescent cells. Protein spots that occurred in the senescent cell samples but not in the non-senescent samples were digested and sent for mass spectrometry analysis for identification.

Example 8 Immunostaining for Cathepsin B Expression on the Surface of Senescent Cells

Senescent fibroblasts and non-senescent fibroblasts were grown on cover slips and immunostained for cell surface expression of cathepsin B. Images appear in FIGS. 5A and 5B, which show surface staining for cathepsin B on the senescent cells but not on their non-senescent counterparts.

Fibroblasts (CCD1070Sk) were grown in culture as detailed herein. Replicatively senescent cells were acquired by growing cells for 50 population doublings followed by plating on cover slips. Non-senescent cells were acquired by plating mid passage fibroblasts on cover slips. Cells on cover slips were allowed to attach overnight. Cells were fixed with methanol and washed. Rabbit polyclonal antibody to cathepsin B was diluted 1:100 in PBS with 0.2% BSA. Cells were incubated with primary antibody to cathepsin B for one hour at room temperature followed by washing three times with cold PBS. Secondary antibody (goat anti rabbit IgG conjugated to FITC) was diluted 1:100 in PBS with 0.2% BSA and used to incubate cells for 30 minutes at room temperature. Cells were washed three times with cold PBS.

Example 9 Materials and Methods

Cell Culture

All cells were obtained from American Type Culture Collection (Manassas, Va.). Each cell culture was grown at 37° C. in 5% CO₂. CCD-1070Sk (fibroblasts) were grown in minimum essential medium (Eagle) with 2 mM L-glutamine and Earle's BSS adjusted to contain 1.5 g/L sodium bicarbonate, 0.1 mM non-essential amino acids, and 1.0 mM sodium pyruvate, and supplemented with 10% fetal bovine serum. RWPE-1 (non-cancerous prostate epithelial cells) were grown in keratinocyte-serum free medium supplemented with 5 ng/mL human recombinant EGF and 0.05 mg/mL bovine pituitary extract.

Chemical induction of cellular senescence

CCD-1070Sk (fibroblasts) was cultured as described above to 70% confluence. Cells were then treated with 200 μM hydrogen peroxide (i.e., H₂O₂) for 2 hours. Media was then replaced with fresh media and cells were allowed to grow for 3 days. Cells were then harvested by trypsinization, split 1:3, and again grown to 70% confluence. Cells were then retreated with 200 μM hydrogen peroxide. Lower passage number fibroblasts frequently required two treatments with hydrogen peroxide, but higher passage fibroblasts occasionally required only a single treatment.

Peptide Synthesis

Peptides were synthesized using standard FMOC protected chemistry. For in vitro cell cytotoxicity studies, peptide was synthesized with a C-terminal, cell lytic sequence according to the following: GVYHFAPLTPTPGGGS(KFAKFAK)₂ (SEQ: ID NO:6; SenL). The peptide sequence GVYHFAPLTPTPGGGC (SEQ ID NO:5; SenC) was synthesized for subsequent conjugation to ricin-A subunit and for radio-labeling with 99m-technetium.

Conjugation of FITC to Peptide

FITC was conjugated to the N terminus of SenC according to the following: (1) A senescent cell binding peptide (SenC; SEQ ID NO:5) was prepared at a concentration of 5 mM in 125 μL of 0.5 M NaHCO₃ buffer, pH 9.5, and (2) FITC was added to the peptide solution at a 1:5 molar ratio (peptide:FITC) and diluted to a final volume of 200 μL. The solution was incubated in the dark for 2 hours. Peptide-FITC conjugate was purified on a P4 column using PBS, pH 7.2 as an eluent.

Cell Internalization

Premature senescence of fibroblasts (CCD-1070Sk) was induced as outlined above. Non-senescent fibroblasts were grown in culture as detailed above. Cells were harvested and added to collagen-coated coverslips and grown in MEM plus 10% FBS overnight. Media was removed, and cells were washed once with PBS. Minimal essential media without FBS was added to the cells. A senescent cell binding peptide (SenC; SEQ ID NO:5) conjugated to FITC was added to cells on coverslips at a concentration of 5 μM and incubated for 3 hours. Cells were than washed five times with PBS followed by fixation with 1:1 methanol/acetone for 10 minutes at −20° C. Coverslips were air dried and mounted in fluorescent mounting media with DAPI and visualized with an Olympus BX51 fluorescent microscope and DP70 digital camera with excitation and emission wavelengths of 490 and 520 nm.

Cytotoxicity of Senescent Cell Binding Peptide Conjugated to a Lytic Peptide Sequence

CCD-1070Sk and RWPE-1 were grown in culture as detailed above. Premature senescence of fibroblasts was chemically induced as described above. Cells were trypsinated and suspended in culture media containing 10% FBS. Cells were centrifuged at 1,000 rpm for 5 minutes. Supernatant was removed and cells were resuspended in 1 mL media without FBS. Cell suspensions were diluted to 20,000 cells/75 μL. Twenty-five microliters of appropriately-diluted agent solution (SenL; SEQ ID NO:6) was added to cell samples to give various concentrations of 0, 0.1, 0.5, 1.0, 2.5, 5.0 or 10 μM. Each sample was prepared in triplicate. Cell suspensions were transferred to a 96 well plate and incubated in the presence of various concentrations of SenL for 2 hours at 37° C. Six samples of each cell type contained no agent. The assay plate was removed from the incubator, and 2 μL of lysis solution (Tris 25 mM, pH 7.5, 0.5% triton X-100) was added to three samples of each cell type without agent to generate a positive control maximum LDH release. LDH release was measured in each sample by adding 100 μL of CytoTox-ONE Reagent (Roche Applied Science) to each well and mixing on a plate shaker for 30 seconds. Samples were incubated at 22° C. for 10 minutes. The reaction was terminated by adding 50 μL of Stop Solution (per 100 μL of CytoTox-ONE™ Reagent added) to each well. Fluorescence was measured in each well using an excitation wavelength of 530 nm and an emission wavelength of 620 nm (Cytofluor 4000). The CytoTox-ONE assay was shown to yield a quantity of fluorescent product that is linearly proportional to the number of cells killed (correlation coefficient=0.99). The percentage of cells killed was calculated using the following formula:

${\%\mspace{14mu}{cytotoxicity}} = \frac{100\% \times \left( {P - C} \right)}{\left( {M - C} \right)}$ where P=LDH release in wells of peptide incubated cells; C=LDH release in wells of cells not incubated with peptide; and M=LDH release in wells incubated in lysis solution. The formula is based upon the assumptions that, in a linear relationship between CytoTox-ONE product development and number of cells killed, C is the y-intercept, and M is due to 100% cell killing. Effect of SenL on Cell Proliferation

Cell proliferation was assayed using the Cell Proliferation Reagent WST-1 (Roche, Mannheim, Germany) by following the manufacturer's instructions.

In Vitro Cytotoxicity: Conjugation to Ricin-A

Peptide SenC (GVYHFAPLTPTPGGGC; SEQ ID NO:5) was conjugated to ricin A subunit (Sigma-Aldrich) to form SenR. Ricin A was obtained from manufacturer in solution. A buffer exchange was performed with 0.1 M PBS/20% glycerol. Ricin A was conjugated with NHS-PEO₄-maleimide cross linker (Pierce, Rockford, Ill.) at a 1:10 molar ratio for 30 minutes at room temperature. Derivatized ricin A was purified on a P4 column using 0.1 M PBS/20% glycerol as an elution buffer. Derivatized ricin A was combined with P12S at a 1:1 molar ratio and reacted for 2 hours at room temperature.

CCD-1070Sk and RWPE-1 were grown in culture as detailed above. Senescence was chemically-induced as described above. Cells were trypsinized and suspended in culture media containing 10% FBS. Cells were centrifuged at 1,000 rpm for 5 minutes. Supernatant was removed and cells were resuspended in 1 mL media without FBS. Cell suspensions were diluted to 20,000 cells/75 μL. Twenty-five microliters of appropriately-diluted peptide-ricin A conjugate was added to each cell sample to give various concentrations. Each sample was prepared in triplicate. Cell suspensions were transferred to a 96 well plate and incubated in the presence of peptide-ricin A conjugate for 2 hours at 37° C. Percentage of cells killed (FIG. 3) was determined as outlined above.

Radio-Labeling of Peptide Senescent Cell binding peptide

A senescent cell binding agent (SEQ ID NO:1) was conjugated at its C terminus to the linker sequence GGGC (SEQ ID NO:9) by synthesizing both as a single construct (i.e., SenC; SEQ ID NO:5). The purpose of attaching GGGC was that it can be used to chelate reduced 99m-Tc for radio-labeling. A 2 μL aliquot of conjugated senescent cell binding agent (3 M) was mixed with 40 μL of 0.25 M ammonium acetate, 15 μL of tartrate buffer pH 8.7, 4 μL of stannous chloride in 100 mM of sodium tartrate, and 30 μL of 99m-Tc pertechnetate. The mixture was heated for 25 minutes at 95° C. Quality control was performed with Sep-Pak and was always above 90% purity. A small aliquot was also injected on a Waters 600 HPLC to check the radiological profile. Fractions were collected and read on a gamma counter (Perkin-Elmer Wallac Wizard 1470).

Cell Binding Assay

Binding of radio-labeled SenC (SEQ ID NO:5) to senescent and non-senescent cells was tested by competition with unlabeled SenC. Peptide solutions were prepared to contain 0 or 20 μM of unlabeled SenC, 15 nM radio-labeled SenC, and 0.2% BSA. Chemically-induced senescent fibroblasts, their non-senescent counterparts, and prostate epithelial cells were prepared as above, harvested, and centrifuged. The cell pellets were resuspended in fresh media without FBS, and cells were counted. Peptide solution containing 0 or 20 μM unlabeled SenC and constant concentrations of SenC and 10⁵ senescent cells were combined in a final volume of 200 μL of PBS in Eppendorf tubes and incubated for 4 hours. Cells were pelleted by centrifuging at 2500 rpm for 2 minutes and washed twice with PBS and 0.2% BSA. Pellets were suspended in 5 μL PBS and transferred to 12×75 mm tubes for counting radioactivity using a gamma counter (Perkin-Elmer Wallac Wizard 1470).

Other Embodiments

All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each independent publication or patent application was specifically and individually indicated to be incorporated by reference.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure that come within known or customary practice within the art to which the invention pertains and may be applied to the essential features hereinbefore set forth. 

The invention claimed is:
 1. A method for specifically delivering a compound to a senescent cell, the method comprising: obtaining a conjugate, wherein the conjugate includes the compound conjugated to a senescent cell binding peptide that contains a senescent cell binding sequence; and contacting the cell with the conjugate; thereby specifically delivering the compound to the senescent cell; wherein the senescent cell binding peptide configures the conjugate to bind preferentially to senescent cells characterized as expressing senescence associated beta-galactosidase, in comparison with cells not expressing senescence associated beta-galactosidase; and wherein the senescent cell binding sequence is selected from SEQ. ID NOS: 1, 2, and
 3. 2. The method of claim 1, wherein the compound is a cytotoxic or lytic agent.
 3. The method of claim 2, which is a method for specifically killing a senescent cell.
 4. The method of claim 2, wherein the cytotoxic or lytic agent is a peptide.
 5. The method of claim 4, wherein the cytotoxic or lytic peptide contains SEQ. ID NO: 4 or the ricin A subunit.
 6. The method of claim 4, wherein the conjugate is a fusion protein that includes the senescent cell binding peptide conjugated to the cytotoxic peptide by way of a linker peptide selected from SEQ. ID NO:9 and SEQ. ID NO:10.
 7. The method of claim 1, wherein the compound is a cytotoxic or therapeutic moiety that is not a peptide.
 8. The method of claim 7, wherein the cytotoxic or therapeutic moiety is a fluorochrome.
 9. The method of claim 1, wherein the cell is contacted with the conjugate in vitro.
 10. A method of preparing a conjugate that is configured to specifically deliver a compound to a senescent cell in accordance with claim 1, the method comprising: obtaining a senescent cell binding peptide that contains the senescent cell binding sequence; obtaining the compound; and conjugating the senescent cell binding peptide to the compound to form a conjugate; whereby the senescent cell binding peptide configures the conjugate to bind preferentially to senescent cells characterized as expressing senescence associated beta-galactosidase, in comparison with cells not expressing senescence associated beta-galactosidase.
 11. The method of claim 10, wherein the compound is a cytotoxic or lytic agent.
 12. A conjugate that is configured to specifically deliver a compound to a senescent cell in accordance with claim 1, wherein the conjugate comprises: a senescent cell binding peptide that contains said senescent cell binding sequence; and said compound; wherein the compound is conjugated to the senescent cell binding peptide in such a manner that the conjugate resulting therefrom binds specifically to senescent cells characterized as expressing senescence associated beta-galactosidase, in comparison with cells not expressing senescence associated beta-galactosidase.
 13. The conjugate of claim 12, wherein the compound is a cytotoxic or lytic agent.
 14. A method for identifying a senescent cell binding polypeptide having a binding specificity that is effective for specifically delivering a compound to a senescent cell, the method comprising: obtaining a library of polypeptides for testing as potential senescent cell binding agents; obtaining a population of senescent cells that are characterized as being non-cancer cells that express both p16 and senescence associated beta-galactosidase; contacting the senescent cells with polypeptides from the library; contacting non-senescent cells with polypeptides from the library; and identifying one or more polypeptides from the library that have bound to the senescent cells but not the non-senescent cells as senescent cell binding agents having a binding specificity that is effective for specifically delivering a compound to a senescent cell.
 15. The method of claim 14, comprising: contacting non-senescent cells with polypeptides from the library; and recovering polypeptides that have not bound to the non-senescent cells in the preceding step, thereby producing a subtraction library; contacting senescent cells with polypeptides from the subtraction library; and recovering polypeptides that have bound to the senescent cells in the preceding step; thereby producing a library of polypeptides that are identified as senescent cell binding agents having a binding specificity that is effective for specifically delivering a compound to a senescent cell.
 16. The method of claim 14, further comprising sequencing one or more of the polypeptides identified as being senescent cell binding agents, thereby obtaining a senescent cell binding sequence for each of the sequenced polypeptides.
 17. The method of claim 16, further comprising determining a consensus sequence from a plurality of the senescent cell binding sequences.
 18. The method of claim 14, further comprising conjugating a compound to be delivered to a senescent cell to at least one of said identified polypeptides. 